pc: reserve more memory for ACPI for new machine types

commit 868270f23d8db2cce83e4f082fe75e8625a5fbf9
    acpi-build: tweak acpi migration limits
broke kernel loading with -kernel/-initrd: it doubled
the size of ACPI tables but did not reserve
enough memory.

As a result, issues on boot and halt are observed.

Fix this up by doubling reserved memory for new machine types.

Cc: qemu-stable@nongnu.org
Reported-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
