FM Radio: do not try to change thread priority

The FM Radio services try to change the current thread when
instantiated, for unknown reason. This actually ends up changing the
priority of SystemServer's main thread. Probably a bad idea. This is
the cause of the various glitch fallout after the FM Radio merges.

Change-Id: I292aff3380c717ff1bc7d45f6303c0d330ef642d
FM Radio: avoid deadlock when disabling RDS

When RDS is being configured, the session mutex is hold. However,
when it is being disabled, RDS callbacks might still fire, and these
also try to hold the mutex, leading to a deadlock.

Temporary unlock the mutex while the vendor library is called to
work around.

Change-Id: Ic9751c7185fd8de4a7510225f54d23a22f042321