Integrate nxmutex support fully into nxsem

This puts the mutex support fully inside nxsem, allowing
locking the mutex and setting the holder with single atomic
operation.

This enables fast mutex locking from userspace, avoiding taking
critical_sections, which may be heavy in SMP and cleanup
of nxmutex library in the future.

Signed-off-by: Jukka Laitinen <jukka.laitinen@tii.ae>

libs/libc/semaphore/sem_wait.c

@@ -30,6 +30,7 @@
 #include <assert.h>
 #include <sched.h>
 
+#include <nuttx/sched.h>
 #include <nuttx/init.h>
 #include <nuttx/cancelpt.h>
 #include <nuttx/semaphore.h>
@@ -156,8 +157,9 @@ int nxsem_wait(FAR sem_t *sem)
 #  endif
       )
     {
-      int32_t old = 1;
-      if (atomic_try_cmpxchg_acquire(NXSEM_COUNT(sem), &old, 0))
+      int32_t tid = _SCHED_GETTID();
+      int32_t old = NXSEM_NO_MHOLDER;
+      if (atomic_try_cmpxchg_acquire(NXSEM_MHOLDER(sem), &old, tid))
         {
           return OK;
         }