sf: Fix incorrect state reporting in dumpsys

Dumpsys utility accesses layer compositionType variable
with out proper protection. These variables are modified
during hwc_prepare call. Existing HAL lock protection is not
sufficient to address this issue. Failure to do this will
result in incorrect state reporting in dumpsys.

A new displayLock mutex in HWComposer will be used in both
dumpsys and draw calls to ensure correct state is accessed.

Change-Id: I8a57de59525adc0e089b3bed95c067c01e42b666