report serial devices created with -device in the PIIX4 config space

Serial and parallel devices created with -device are not reported in
the PIIX4 configuration space, and are hence not picked up by the DSDT.
This upsets Windows, which hides them altogether from the guest.

To avoid this, check at the end of machine initialization whether the
corresponding I/O ports have been registered.  The new function in
ioport.c does this; this also requires a tweak to isa_unassign_ioport.

I left the comment in piix4_pm_initfn since the registers I moved do
seem to match the 82371AB datasheet.  There are some quirks though.
We are setting this bit:

    "Device 8 EIO Enable (EIO_EN_DEV8)—R/W. 1=Enable PCI access to the
    device 8 enabled I/O ranges to be claimed by PIIX4 and forwarded
    to the ISA/EIO bus. 0=Disable. The LPT_MON_EN must be set to enable
    the decode."

but not LPT_MON_EN (bit 18 at 50h):

    LPT Port Enable (LPT_MON_EN)—R/W. 1=Enable accesses to parallel
    port address range (LPT_DEC_SEL) to generate a device 8 (parallel
    port) decode event. 0=Disable.

We're also setting the LPT_DEC_SEL field (that's the 0x60 written to
63h) to 11, which means reserved, rather than to 01 (378h-37Fh).

Likewise we're not setting SA_MON_EN, SB_MON_EN (respectively bit 14
and bit 16 at address 50h) for the serial ports.  However, we're setting
COMA_DEC_SEL and COMB_DEC_SEL correctly, unlike the corresponding register
for the parallel port.

All these fields are left as they are, since they are probably only
meant to be used in the DSDT.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
