SF: Fix thread safety in ISurfaceComposer APIs

Fix a few cases of ISurfaceComposer functions looking up displays and
calling into HWC without holding mStateLock. Clean up error handling
for consistent messages and accurate status codes.

Bug: 123715322
Test: Boot (no repro, just an audit)
Change-Id: I6432e15c4166b27398137b681b4ea7c056fea5e4