extract/unify the constant 0xfee00000 as APIC_DEFAULT_ADDRESS

A common dependency of the constant's current users:
- hw/apic_common.c
- hw/i386/kvmvapic.c
- target-i386/cpu.c
is "target-i386/cpu.h".

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1363821803-3380-9-git-send-email-lersek@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>