Add support for mlockall() and munlockall(). These two functions
comprise the _POSIX_MEMLOCK Option which is required by PSE51,
PSE52, PSE53, and PSE54.
Zephyr's on-demand paging API does not yet support pinning and
unpinning *all* virtual memory regions, so these functions are
expected to fail, setting errno to ENOSYS. Any other usage is
currently categorized as undefined behaviour.
Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>