crypto: Add missing MODULE_DESCRIPTION() macros

Fix the 'make W=1' warnings:
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/cast_common.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/af_alg.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/algif_hash.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/algif_skcipher.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/ecc.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/curve25519-generic.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/xor.o
WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/crypto_simd.o

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>