msm: mdss: Disable footswitch during idle pc

Besides turning off clocks/BW in idle state, footswitch can also be
disabled on cmd mode panels. This is triggered based on pm runtime
callbacks and count of active overlay sessions.

Change-Id: I5c69209f2ee79fe2a7c3f87c01ff21ecf8e367d7
Signed-off-by: Sravanthi Kollukuduru <skolluku@codeaurora.org>