kvmvapic: add ioport read accessor

Necessary since memory region accessor assumes read and write
methods are registered. Otherwise reading I/O port 0x7e segfaults.

https://bugzilla.redhat.com/show_bug.cgi?id=954306

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
