nanokernel: Add nano_sem_count_get for getting nano_sem count

This adds convenient helper so that users don't need to touch nano_sem
internals. Wrapper for unified kernel is added too.

Change-Id: Ic0af8b1ea302939d5239648327cb3cc125c48148
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>
2 files changed