posix: use sys_sem instead of k_spinlock for pool synch

Based on Andy's talk at eoss 2024, use the sys/sem.h api instead
of the spinlock.h api to synchronize pooled elements since it
has minimal overhead like semaphores but also works from
userspace.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
4 files changed