drm/msm: COMPILE_TEST support

With a simple stub, we can get COMPILE_TEST support.

Signed-off-by: Rob Clark <robdclark@gmail.com>

diff --cc drivers/gpu/drm/msm/Kconfig
Simple merge

diff --cc drivers/gpu/drm/msm/mdp4/mdp4_dtv_encoder.c
Simple merge

diff --cc drivers/gpu/drm/msm/msm_drv.h
Simple merge