register reset handler for option_roms

Currently, boot options are not preserved across a system reset.
option roms can modify themselves, or can for instance restore the real
int 0x19 vector after they tried to boot from it.

To properly do that, we need a reset handler registered to deal with option
roms. This patch is based on current version on qemu-kvm.git

Signed-off-by: Glauber Costa <glommer@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>