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