Bump Surfaceflinger's binder threads to SCHED_FIFO

1) Set threads in Surfaceflinger's threadpool to have SCHED_FIFO policy
(and lowest RT priority). This is achieved by temporarily promoting the
priority of the thread creating the threadpool to the aforementioned
configuration.

2) Also set the minimum policy for the SF binder node to be SCHED_FIFO.

Test: presubmit
Bug: 183129340
Change-Id: I2df47fdc00fb0ae8937c30710243305cf018d830