OvmfPkg: fold macros of unsupported PM2 control reg. block into Facp.aslc

OvmfPkg: fold macros of unsupported PM2 control reg. block into Facp.aslc

Soon we're going to specify Extended Addresses of register blocks in
Generic Address Structure format. The GAS is easy to fill if we want to
posit either "unsupported" (all zero) or a given address in a specific
address space. However deriving "unsupported" just from a macro expanding
to zero is unwieldy, so let's avoid the need.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14153 6f19259b-4bc3-4df7-8a09-765794883524