drivers/intel/gma: Fix OpRegion Mailbox3 synchronization

Make XBCM `Serialized` (obvious), and check for the callee clearing the
request bit (we checked only the status for 0 which we potentially wrote
ourselves).

Change-Id: Ic92d525eda8d0a159fa5ddaacf230658d71c1578
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/28302
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

0 files changed, 0 insertions, 0 deletions