[libc] Add inline assembly implementation of flsl() using BSR instruction

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/bitops.c

@@ -1,13 +0,0 @@
-#include <strings.h>
-
-FILE_LICENCE ( GPL2_OR_LATER );
-
-int __flsl ( long x ) {
-	unsigned long value = x;
-	int ls = 0;
-
-	for ( ls = 0 ; value ; ls++ ) {
-		value >>= 1;
-	}
-	return ls;
-}