sdm: Proper handing of CRTC set and reset.

- Power-on will set the CRTC_SET_MODE to valid on external display.
  Without first commit, if external is disconnected, CRTC_SET_MODE
  is not set to NULL, this leads to a synchronization issue and
  external is blank for sometime. So on successful power-on
  (i.e NullCommit),set CRTC_SET_MODE to NULL for proper sync.

Change-Id: I48a009d75f4c777ed8ad20b55de66bfd37feeeb1
CRs-Fixed: 2677136
2 files changed