libbinder: setMinSchedulerPolicy

This function on BBinder allows the minimum scheduling priority for
incoming binder transactions to be set by the binder driver. This
functionality was originally developed for libhwbinder and ported here.
The main difference from libhwbider is that invalid priority sets cause
an abort, whereas for libhwbinder, an error is returned. Unfortunately,
that error is frequently ignored, and since this reflects static
configuration, abort is considered a benefit.

Bug: 149933095
Test: binderLibTest
Change-Id: Ie93aebb09f4142cd66d841ca8b3ca39d1e0bb75e