gma500: Consider CRTC initially active.

[this one ideally should make 3.6 - it fixes the very annoying mode setting bug]

This causes the pipe to be forced off prior to initial mode set, which
roughly mirrors the behavior of the i915 driver.  It fixes initial mode
setting on my Intel DN2800MT (Cedarview) board.  Without it, mode
setting triggers an out-of-range error from the monitor for most modes,
but only on initial configuration (i.e. they can be configured
successfully from userspace after that).

Signed-off-by: Forest Bond <forest.bond@rapidrollout.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>