lib/crc: document all the CRC library kconfig options

Previous commits removed all the original CRC kconfig help text, since
it was oriented towards people configuring the kernel, and the options
are no longer user-selectable.  However, it's still useful for there to
be help text for kernel developers.  Add this.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Martin K. Petersen" <martin.petersen@oracle.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250401221600.24878-7-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

Author: ebiggers

lib/Kconfig

@@ -140,12 +140,21 @@ source "lib/crypto/Kconfig"
 
 config CRC_CCITT
 	tristate
+	help
+	  The CRC-CCITT library functions.  Select this if your module uses any
+	  of the functions from <linux/crc-ccitt.h>.
 
 config CRC16
 	tristate
+	help
+	  The CRC16 library functions.  Select this if your module uses any of
+	  the functions from <linux/crc16.h>.
 
 config CRC_T10DIF
 	tristate
+	help
+	  The CRC-T10DIF library functions.  Select this if your module uses
+	  any of the functions from <linux/crc-t10dif.h>.
 
 config ARCH_HAS_CRC_T10DIF
 	bool
@@ -156,10 +165,16 @@ config CRC_T10DIF_ARCH
 
 config CRC_ITU_T
 	tristate
+	help
+	  The CRC-ITU-T library functions.  Select this if your module uses
+	  any of the functions from <linux/crc-itu-t.h>.
 
 config CRC32
 	tristate
 	select BITREVERSE
+	help
+	  The CRC32 library functions.  Select this if your module uses any of
+	  the functions from <linux/crc32.h> or <linux/crc32c.h>.
 
 config ARCH_HAS_CRC32
 	bool
@@ -170,6 +185,9 @@ config CRC32_ARCH
 
 config CRC64
 	tristate
+	help
+	  The CRC64 library functions.  Select this if your module uses any of
+	  the functions from <linux/crc64.h>.
 
 config ARCH_HAS_CRC64
 	bool
@@ -180,9 +198,15 @@ config CRC64_ARCH
 
 config CRC4
 	tristate
+	help
+	  The CRC4 library functions.  Select this if your module uses any of
+	  the functions from <linux/crc4.h>.
 
 config CRC7
 	tristate
+	help
+	  The CRC7 library functions.  Select this if your module uses any of
+	  the functions from <linux/crc7.h>.
 
 config LIBCRC32C
 	tristate
@@ -193,6 +217,9 @@ config LIBCRC32C
 
 config CRC8
 	tristate
+	help
+	  The CRC8 library functions.  Select this if your module uses any of
+	  the functions from <linux/crc8.h>.
 
 config CRC_OPTIMIZATIONS
 	bool "Enable optimized CRC implementations" if EXPERT