x86, apic: Move SGI UV functionality out of generic IO-APIC code

Move UV specific functionality out of the generic IO-APIC code.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
LKML-Reference: <20091013203236.GD20543@sgi.com>
[ Cleaned up the code some more in their new places. ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>