drm/msm: move helper calls to msm_kms.c

Extract two more KMS-related codepieces to msm_kms.c, removing last
pieces of KMS code from msm_drv.c.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/662574/


Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>