pragma once and for all

libsel4sync: Move OS agnostic to platsupport

Fix licenses

libsel4sync: replaced aep with notification

The only non-local changes in this commit are renaming of fields of
sync_bin_sem_t and sync_recursive_mutex_t from aep to notification.
Nothing outside of this library should operate on those fields directly.

libsel4sync: Move the implementation of bare binary semaphores to headers.

This change allows the bare binary semaphore operations to be inlined into
calling code. The effect of this commit has not been quantified, but the result
for any calling code should be increased or unaffected performance. Semantics of
the operations is unchanged.