disp: msm: fix driver unload issues in gki config

Resolves segmentation fault during driver unload in GKI
configuration, caused by repeated debugfs destroy calls.
Also removes redundant unload calls.

Change-Id: I20a8efc1916b9a60766f9c7714a4b458aa518566
Signed-off-by: Orion Brody <obrody@codeaurora.org>