Revert "fsverity: relax build time dependency on CRYPTO_SHA256"

This reverts commit e3a606f because it
allows people to create broken configurations that enable FS_VERITY but
not SHA-256 support.

The commit did allow people to disable the generic SHA-256
implementation when it's not needed.  But that at best allowed saving a
bit of code.  In the real world people are unlikely to intentionally and
correctly make such a tweak anyway, as they tend to just be confused by
what all the different crypto kconfig options mean.

Of course we really need the crypto API to enable the correct
implementations automatically, but that's for a later fix.

Acked-by: Ard Biesheuvel <[email protected]>
Cc: Herbert Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Eric Biggers <[email protected]>

Author: ebiggers

fs/verity/Kconfig

@@ -4,13 +4,9 @@ config FS_VERITY
 	bool "FS Verity (read-only file-based authenticity protection)"
 	select CRYPTO
 	select CRYPTO_HASH_INFO
-	# SHA-256 is implied as it's intended to be the default hash algorithm.
+	# SHA-256 is selected as it's intended to be the default hash algorithm.
 	# To avoid bloat, other wanted algorithms must be selected explicitly.
-	# Note that CRYPTO_SHA256 denotes the generic C implementation, but
-	# some architectures provided optimized implementations of the same
-	# algorithm that may be used instead. In this case, CRYPTO_SHA256 may
-	# be omitted even if SHA-256 is being used.
-	imply CRYPTO_SHA256
+	select CRYPTO_SHA256
 	help
 	  This option enables fs-verity.  fs-verity is the dm-verity
 	  mechanism implemented at the file level.  On supported