msm: board-8930: Keep the GPU power rail on when display is on

Do not allow the GPU to go into SLUMBER while the display is still
on. This fixes issues seen on 8930 when this feature is enabled.

Change-Id: I8c76d1297c2215987bdd493cb9f04d45d9ec87dc
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>