OvmfPkg: new macros for platform specific register addresses and values

OvmfPkg: new macros for platform specific register addresses and values

Define some new macros for register addresses (both PCI and IO) and
register values (bits) that we're going to use soon.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Gabriel Somlo <somlo@cmu.edu>
Tested-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17433 6f19259b-4bc3-4df7-8a09-765794883524