KVM: Portability: move get/set_apic_base to x86.c

This patch moves the implementation of get_apic_base and set_apic_base
from kvm_main.c to x86.c

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>