OvmfPkg: fold macros of unsupported GPE1 register block into Facp.aslc

OvmfPkg: fold macros of unsupported GPE1 register block into Facp.aslc

In the next patch 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@14154 6f19259b-4bc3-4df7-8a09-765794883524