FreeBSD: Remove HAVE_INLINE_FLSL use

These macros are deprecated in FreeBSD kernel for several years,
and unneeded for much longer.  Instead, similar to Linux, let
kernel let compiler do the right things.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes openzfs#18004

Author: amotin

include/os/freebsd/spl/sys/sysmacros.h

@@ -290,80 +290,11 @@ extern unsigned char bcd_to_byte[256];
 #define	offsetof(type, field)	__offsetof(type, field)
 #endif
 
-/*
- * Find highest one bit set.
- *      Returns bit number + 1 of highest bit that is set, otherwise returns 0.
- * High order bit is 31 (or 63 in _LP64 kernel).
- */
-static __inline int
-highbit(ulong_t i)
-{
-#if defined(HAVE_INLINE_FLSL)
-	return (flsl(i));
-#else
-	int h = 1;
+#define	highbit(x)		flsl(x)
+#define	lowbit(x)		ffsl(x)
 
-	if (i == 0)
-		return (0);
-#ifdef _LP64
-	if (i & 0xffffffff00000000ul) {
-		h += 32; i >>= 32;
-	}
-#endif
-	if (i & 0xffff0000) {
-		h += 16; i >>= 16;
-	}
-	if (i & 0xff00) {
-		h += 8; i >>= 8;
-	}
-	if (i & 0xf0) {
-		h += 4; i >>= 4;
-	}
-	if (i & 0xc) {
-		h += 2; i >>= 2;
-	}
-	if (i & 0x2) {
-		h += 1;
-	}
-	return (h);
-#endif
-}
-
-/*
- * Find highest one bit set.
- *	Returns bit number + 1 of highest bit that is set, otherwise returns 0.
- */
-static __inline int
-highbit64(uint64_t i)
-{
-#if defined(HAVE_INLINE_FLSLL)
-	return (flsll(i));
-#else
-	int h = 1;
-
-	if (i == 0)
-		return (0);
-	if (i & 0xffffffff00000000ULL) {
-		h += 32; i >>= 32;
-	}
-	if (i & 0xffff0000) {
-		h += 16; i >>= 16;
-	}
-	if (i & 0xff00) {
-		h += 8; i >>= 8;
-	}
-	if (i & 0xf0) {
-		h += 4; i >>= 4;
-	}
-	if (i & 0xc) {
-		h += 2; i >>= 2;
-	}
-	if (i & 0x2) {
-		h += 1;
-	}
-	return (h);
-#endif
-}
+#define	highbit64(x)		flsll(x)
+#define	lowbit64(x)		ffsll(x)
 
 #ifdef	__cplusplus
 }