drm/msm: skip commit when handling pm suspend if no crtcs active

Avoid submitting a commit that mentions no CRTCs in the case
where all the CRTCs are already inactive or not in DPMS_ON
state when handling PM suspend.

Change-Id: I4574cce433cc05a39f225e56f49ce4b8d01d59ba
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>