msm: mdss: add valid data checks in ctl restore

Idle power collapse API calls ctl restore for
each control which is powered on. This check will
pass for rotator ctls also. They have valid mixer
but mfd/panel_data null. Only mixer check is invalid
to call pp_resume for such ctls. It should check
the mfd/panel_data before restoring post processing
and compression block.

Change-Id: I09d599aae392e30d9ffae3cfd0e92bbda9aaa5e5
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>