ANDROID: mmc: move to a SCHED_FIFO thread

Running mmcqd as a prio 120 thread forces it to compete with standard
user processes for IO performance, especially when the system is under
severe CPU load. Move it to a SCHED_FIFO thread to reduce the impact of
load on IO performance.

Signed-off-by: Tim Murray <timmurray@google.com>

Based on commits:
 https://github.com/halaszk/Perseus-halaszk-universal5433/commit/4ce1b9334de8836459aba6bbad274a132090a405
 https://github.com/halaszk/Perseus-halaszk-universal5433/commit/8fac35c4045742a59f93c8442f95219fc5c8dff1