OvmfPkg/Library/AcpiTimerLib: Modified to support Xen HVM
OvmfPkg/Library/AcpiTimerLib: Modified to support Xen HVM

If PIIX4 Power Management Base Address (PMBA) is already
programmed, then read and use it's current setting.

Signed-off-by: Andrei Warkentin <andreiw@motorola.com>
Reviewed-by: gavinguan
Signed-off-by: jljusten

git-svn-id: 5648d1bec6962b0a6d1d1b40eba8cf5cdb62da3d@12053 6f19259b-4bc3-4df7-8a09-765794883524

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2