Add IT8721F support

Add IT8721F support

only the serial port is tested, keyboard/mouse are gonna
to be tested later, it may also need some more patches
to make it work completely.

Change-Id: Ie9464d01c5d5760ebc800b3cd15a4ab2bad2e09f
Signed-off-by: QingPei Wang <wangqingpei@gmail.com>
Reviewed-on: http://review.coreboot.org/204
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>