drm/msm: allow flags to be set in property helpers

Expand API for property helper functions to allow passing in
more DRM flags, specifically to allow DRM_MODE_PROP_IMMUTABLE
to be declared.

Change-Id: I17b48412488f8ca7e32d6bda9e5089c560d1f711
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>