x86, apic: Move irq_remapping_enabled checks into IRQ-remapping code

Move the three easy to move checks in the x86' apic.c file
into the IRQ-remapping code.

Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>