Move reverse_bits*() to separate source file

reversing bits is not NR specific. Think of it like this: LTE code might
use reverse_bits*() as well, but in the old location, it would pull in a
bunch of NR dependencies that are superfluous.

openair1/PHY/CODING/nrLDPC_coding/nrLDPC_coding_aal/nrLDPC_coding_aal.c

@@ -5,6 +5,7 @@
 #include "../nrLDPC_coding_interface.h"
 #include "nrLDPC_coding_aal.h"
 #include "PHY/sse_intrin.h"
+#include "reverse_bits.h"
 #include <common/utils/LOG/log.h>
 #define NR_LDPC_ENABLE_PARITY_CHECK