Lock mirrorSurfaceControl

This is to avoid race conditions where the surface is released at the
wrong moment.

Given that mirrorSurfaceControl is a rare operation, locking it should
not be a problem.

Flag: EXEMPT bugfix
Bug: 409713395
Test: presubmit
Change-Id: I491fdb312fb00c33a5798a52bfe7da7a915696e9