x86/platform/uv: Update node present counting

The changes in the UV5 arch shrunk the NODE PRESENT table to just 2x64
entries (128 total) so are in to 64 bit MMRs instead of a depth of 64
bits in an array.  Adjust references when counting up the nodes present.

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/20201005203929.148656-11-mike.travis@hpe.com