OvmfPkg: AcpiTimerLib: Access power mgmt regs based on host bridge type

Pick the appropriate bus:dev.fn for accessing ACPI power management
registers (00:01.3 on PIIX4 vs. 00:1f.0 on Q35) based on the device
ID of the host bridge (assumed always present at 00:00.0).

With this patch, OVMF can boot QEMU's "-machine q35" x86 machine type.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/OvmfPkg@16066 6f19259b-4bc3-4df7-8a09-765794883524