x86/apic/uv: Update the APIC UV OEM check

Optimize the first "SGI" OEM check to return faster if the
system is not an SGI or UV system.

Signed-off-by: Mike Travis <travis@sgi.com>
Acked-by: Hedi Berriche <hedi@sgi.com>
Acked-by: Dimitri Sivanich <sivanich@sgi.com>
Link: http://lkml.kernel.org/r/20150409182628.952357922@asylum.americas.sgi.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>