LinuxKPI: move hex2bin() from kernel.h to new hex.h

New Linux v7.0 drivers include hex.h.  Rather than adding a dummy
header, migrate the kernel.h hex2bin() into hex.h, where it belongs.
Care needs to be taken as the _h2b() helper function is still used by
other bits in kernel.h.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Reviewed by:	emaste, dumbbell
Differential Revision: https://reviews.freebsd.org/D56391

sys/compat/linuxkpi/common/include/linux/hex.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2022-2026 Bjoern A. Zeeb
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#ifndef	_LINUXKPI_LINUX_HEX_H_
+#define	_LINUXKPI_LINUX_HEX_H_
+
+#include <linux/types.h>
+#include <linux/errno.h>
+
+static inline int
+_h2b(const char c)
+{
+
+	if (c >= '0' && c <= '9')
+		return (c - '0');
+	if (c >= 'a' && c <= 'f')
+		return (10 + c - 'a');
+	if (c >= 'A' && c <= 'F')
+		return (10 + c - 'A');
+	return (-EINVAL);
+}
+
+static inline int
+hex2bin(uint8_t *bindst, const char *hexsrc, size_t binlen)
+{
+	int hi4, lo4;
+
+	while (binlen > 0) {
+		hi4 = _h2b(*hexsrc++);
+		lo4 = _h2b(*hexsrc++);
+		if (hi4 < 0 || lo4 < 0)
+			return (-EINVAL);
+
+		*bindst++ = (hi4 << 4) | lo4;
+		binlen--;
+	}
+
+	return (0);
+}
+
+#endif	/* _LINUXKPI_LINUX_HEX_H_ */

sys/compat/linuxkpi/common/include/linux/kernel.h

@@ -56,6 +56,7 @@
 #include <linux/log2.h>
 #include <linux/kconfig.h>
 #include <linux/instruction_pointer.h>
+#include <linux/hex.h>
 
 #include <asm/byteorder.h>
 #include <asm/cpufeature.h>
@@ -305,37 +306,6 @@ linux_ratelimited(linux_ratelimit_t *rl)
 #define	add_taint(x,y)	do {	\
 	} while (0)
 
-static inline int
-_h2b(const char c)
-{
-
-	if (c >= '0' && c <= '9')
-		return (c - '0');
-	if (c >= 'a' && c <= 'f')
-		return (10 + c - 'a');
-	if (c >= 'A' && c <= 'F')
-		return (10 + c - 'A');
-	return (-EINVAL);
-}
-
-static inline int
-hex2bin(uint8_t *bindst, const char *hexsrc, size_t binlen)
-{
-	int hi4, lo4;
-
-	while (binlen > 0) {
-		hi4 = _h2b(*hexsrc++);
-		lo4 = _h2b(*hexsrc++);
-		if (hi4 < 0 || lo4 < 0)
-			return (-EINVAL);
-
-		*bindst++ = (hi4 << 4) | lo4;
-		binlen--;
-	}
-
-	return (0);
-}
-
 static inline bool
 mac_pton(const char *macin, uint8_t *macout)
 {