drm/msm: Nuke dummy gamma_set/get functions

Again the fbdev emulation gamma_set/get functions are only needed for
drivers that try to also use 8bpp paletted mode. Which msm doesn't, so
this is dead code. Let's rip it out.

Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1459331485-28376-7-git-send-email-daniel.vetter@ffwll.ch