x86/platform/uv: Update for UV5 NMI MMR changes

The UV NMI MMR addresses and fields moved between UV4 and UV5
necessitating a rewrite of the UV NMI handler.  Adjust references
to accommodate those changes.

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/20201005203929.148656-13-mike.travis@hpe.com