x86/platform/UV: Add references to access fixed UV4A HUB MMRs

x86/platform/UV: Add references to access fixed UV4A HUB MMRs

Add references to enable access to fixed UV4A (rev2) HUB MMRs.

Signed-off-by: Mike Travis <mike.travis@hpe.com>
Acked-by: Andrew Banman <abanman@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dimitri Sivanich <sivanich@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russ Anderson <rja@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1515440405-20880-4-git-send-email-mike.travis@hpe.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>