x86, UV: new UV genapic functions for x2apic

Add functions that use the infrastructure added by the x2apic code. These
functions were originally stubbed out since the UV code went into the
tree prior to the x2apic code.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>