x86/platform/UV: Ensure uv_system_init is called when necessary

x86/platform/UV: Ensure uv_system_init is called when necessary

Move the check to whether this is a UV system that needs initialization
from is_uv_system() to the internal uv_system_init() function.  This is
because on a UV system without a HUB the is_uv_system() returns false.
But we still need some specific UV system initialization.  See the
uv_system_init() for change to a quick check if UV is applicable. This
change should not increase overhead since is_uv_system() also called
into this same area.

Signed-off-by: Mike Travis <travis@sgi.com>
Reviewed-by: Russ Anderson <rja@hpe.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170125163518.256403963@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>