platform_android: prevent deadlock in droid_swap_buffers

To avoid blocking other EGL calls, release the display mutex before
we enqueue buffer to android frameworks and re-acquire the mutex
upon return.

BUG=b/28654039
TEST=verify pinch zoom no longer causes hangs

Change-Id: I8fcddc9a96d8dc0031bbf9285785ac78f3049ac7
1 file changed