System server: Allow get/setsched to hal_camera domain.

Much like audio, the camera HAL may need to have key threads running
in SCHED_FIFO or similar priority.  Allow system_server to raise
thread priority for camera HALs to make this possible.

Test: Video recording works, with EIS. No logspam about EIS failure.
Bug: 35389145
Change-Id: I1d92f9f10dc3aff22ce56b8b9cc57db043631919