loader: fix handling of custom address spaces when adding ROM blobs

* Commit 3e76099aacb4 ("loader: Allow a custom AddressSpace when loading
  ROMs") introduced the "Rom.as" field:

  (1) It modified the utility callers of rom_insert() to take "as" as a
      new parameter from *their* callers, and set "rom->as" from that
      parameter. The functions covered were rom_add_file() and
      rom_add_elf_program().

  (2) It also modified rom_insert() itself, to auto-assign
      "&address_space_memory", in case the external caller passed -- and
      the utility caller forwarded -- as=NULL.

  Except, commit 3e76099aacb4 forgot to update the third utility caller of
  rom_insert(), under point (1), namely rom_add_blob().

* Later, commit 5e774eb3bd264 ("loader: Add AddressSpace loading support
  to uImages") added the load_uimage_as() function, and the
  rom_add_blob_fixed_as() function-like macro, with the necessary changes
  elsewhere to propagate the new "as" parameter to rom_add_blob():

    load_uimage_as()
      load_uboot_image()
        rom_add_blob_fixed_as()
          rom_add_blob()

  At this point, the signature (and workings) of rom_add_blob() had been
  broken already, and the rom_add_blob_fixed_as() macro passed its "_as"
  parameter to rom_add_blob() as "callback_opaque". Given that the
  "fw_callback" parameter itself was set to NULL (correctly), this did no
  additional damage (the opaque arg would never be used), but ultimately
  it broke the new functionality of load_uimage_as().

* The load_uimage_as() function would be put to use in one of the later
  patches, commit e481a1f63c93 ("generic-loader: Add a generic loader").

* We can fix this only in a unified patch now. Append "AddressSpace *as"
  to the signature of rom_add_blob(), and handle the new parameter. Pass
  NULL from all current callers, except from rom_add_blob_fixed_as(),
  where "_as" has to be bumped to the proper position.

* Note that rom_add_file() rejects the case when both "mr" and "as" are
  passed in as non-NULL. The action that this is apparently supposed to
  prevent is the

    rom->mr = mr;

  assignment (that's the only place where the "mr" parameter is used in
  rom_add_file()). In rom_add_blob() though, we have no "mr" parameter,
  and the actions done on the fw_cfg branch:

    if (fw_file_name && fw_cfg) {
        if (mc->rom_file_has_mr) {
            data = rom_set_mr(rom, OBJECT(fw_cfg), devpath);
            mr = rom->mr;
        } else {
            data = rom->data;
        }

  reflect those that are performed by rom_add_file() too (with mr==NULL):

    if (rom->fw_file && fw_cfg) {
        if ((!option_rom || mc->option_rom_has_mr) &&
            mc->rom_file_has_mr) {
            data = rom_set_mr(rom, OBJECT(fw_cfg), devpath);
        } else {
            data = rom->data;
        }

  Hence we need no additional restrictions in rom_add_blob().

* Stable is not affected as both problematic commits appeared first in
  v2.8.0-rc0.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alistair Francis <alistair.francis@xilinx.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Michael Walle <michael@walle.cc>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Shannon Zhao <zhaoshenglong@huawei.com>
Cc: qemu-arm@nongnu.org
Cc: qemu-devel@nongnu.org
Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6
Fixes: 5e774eb3bd264c76484906f4bd0fb38e00b8090e
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
