lib/crypto: ensure generated *.S files are removed on make clean

lib/crypto: ensure generated *.S files are removed on make clean

make clean does not check the kernel config when removing files. As
such, additions to clean-files under CONFIG_ARM or CONFIG_ARM64 are not
evaluated. For example, when building on arm64, this means that
lib/crypto/arm64/sha{256,512}-core.S are left over after make clean.

Set clean-files unconditionally to ensure that make clean removes these
files.

Fixes: e96cb9507f2d ("lib/crypto: sha256: Consolidate into single module")
Fixes: 24c91b62ac50 ("lib/crypto: arm/sha512: Migrate optimized SHA-512 code to library")
Fixes: 60e3f1e9b7a5 ("lib/crypto: arm64/sha512: Migrate optimized SHA-512 code to library")
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Link: https://lore.kernel.org/r/20250814-crypto_clean-v2-1-659a2dc86302@columbia.edu
Signed-off-by: Eric Biggers <ebiggers@kernel.org>