kernel.h: drop hex.h and update all hex.h users

Remove <linux/hex.h> from <linux/kernel.h> and update all users/callers of
hex.h interfaces to directly #include <linux/hex.h> as part of the process
of putting kernel.h on a diet.

Removing hex.h from kernel.h means that 36K C source files don't have to
pay the price of parsing hex.h for the roughly 120 C source files that
need it.

This change has been build-tested with allmodconfig on most ARCHes.  Also,
all users/callers of <linux/hex.h> in the entire source tree have been
updated if needed (if not already #included).

Link: https://lkml.kernel.org/r/20251215005206.2362276-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

crypto/asymmetric_keys/asymmetric_type.c

@@ -9,6 +9,7 @@
 #include <keys/asymmetric-subtype.h>
 #include <keys/asymmetric-parser.h>
 #include <crypto/public_key.h>
+#include <linux/hex.h>
 #include <linux/seq_file.h>
 #include <linux/module.h>
 #include <linux/overflow.h>

crypto/asymmetric_keys/x509_public_key.c

@@ -10,6 +10,7 @@
 #include <keys/asymmetric-parser.h>
 #include <keys/asymmetric-subtype.h>
 #include <keys/system_keyring.h>
+#include <linux/hex.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>

crypto/krb5/selftest.c

@@ -7,6 +7,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/hex.h>
 #include <linux/slab.h>
 #include <crypto/skcipher.h>
 #include <crypto/hash.h>