x86/platform/UV: Fix 2 socket config problem

x86/platform/UV: Fix 2 socket config problem

A UV4 chassis with only 2 sockets configured can unexpectedly
target the wrong UV hub.  Fix the problem by limiting the minimum
size of a partition to 4 sockets even if only 2 are configured.

Signed-off-by: Mike Travis <travis@sgi.com>
Reviewed-by: Russ Anderson <rja@hpe.com>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170113152111.313888353@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>