OvmfPkg: determine PMBA value dependent on host bridge device ID

OvmfPkg: determine PMBA value dependent on host bridge device ID

In this patch, the AcpiTimerLib instances, ResetSystemLib, and PlatformPei
are modified together in order to keep VMs functional across a bisection:
they all must agree on the PMBA value used.

ResetSystemLib must not use dynamic PCDs. With SOURCE_DEBUG_ENABLE, it
gets linked into the debug agent, therefore the same restrictions apply to
it as to BaseRomAcpiTimerLib. Luckily, AcpiPmControl() is only used for
powering off the virtual machine, thus the extra cost of a PCI config
space read, compared to a PcdGet16(), should be negligible.

This is the patch that moves the PMBA to IO port 0x0600 on Q35 in
practice.

The ResetSystemLib change is easiest to verify with the "reset -s" command
in the UEFI shell (which goes through gRT->ResetSystem() and, in OVMF,
PcAtChipsetPkg/KbcResetDxe).

Cc: Gabriel Somlo <somlo@cmu.edu>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1333238
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Gabriel Somlo <somlo@cmu.edu>