kvm: Use APIC_DEFAULT_PHYS_BASE macro as the apic access page address.

We have APIC_DEFAULT_PHYS_BASE defined as 0xfee00000, which is also the address of
apic access page. So use this macro.

Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Reviewed-by: Gleb Natapov <gleb@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>