Revert "fscrypt: relax Kconfig dependencies for crypto API algorithms"

Revert "fscrypt: relax Kconfig dependencies for crypto API algorithms"

This mostly reverts commit a0fc20333ee4bac1147c4cf75dea098c26671a2f.
Keep the relevant parts of the comment added by that commit.

The problem with that commit is that it allowed people to create broken
configurations that enabled FS_ENCRYPTION but not the mandatory
algorithms.  An example of this can be found here:
https://lore.kernel.org/r/1207325.1737387826@warthog.procyon.org.uk/

The commit did allow people to disable specific generic algorithm
implementations that aren't 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 <ardb@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://lore.kernel.org/r/20250217185314.27345-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>