crypto: crc32 - don't unnecessarily register arch algorithms

Instead of registering the crc32-$arch and crc32c-$arch algorithms if
the arch-specific code was built, only register them when that code was
built *and* is not falling back to the base implementation at runtime.

This avoids confusing users like btrfs which checks the shash driver
name to determine whether it is crc32c-generic.

(It would also make sense to change btrfs to test the crc32_optimization
flags itself, so that it doesn't have to use the weird hack of parsing
the driver name.  This change still makes sense either way though.)

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20241202010844.144356-5-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@google.com>