x86/platform/uv: Adjust GAM MMR references affected by UV5 updates

Make modifications to the GAM MMR mappings to accommodate changes for UV5.

Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Reviewed-by: Steve Wahl <steve.wahl@hpe.com>
Link: https://lkml.kernel.org/r/20201005203929.148656-9-mike.travis@hpe.com