drm/msm/dsi-staging: avoid DMS on CRTC active change

When CRTC active state changes, DRM object's disable/enable API's need to
invoked to transit the objects into relevant states. Since DMS is bound to
bypass some of these API's, avoid setting the DMS mode flag on
CRTC active changes.

Change-Id: I0653638cefad312b90918bcd1f659fe8bf873a0a
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>