crypto: x86/serpent - stop using the SIMD helper

crypto: x86/serpent - stop using the SIMD helper

Stop wrapping skcipher and aead algorithms with the crypto SIMD helper
(crypto/simd.c).  The only purpose of doing so was to work around x86
not always supporting kernel-mode FPU in softirqs.  Specifically, if a
hardirq interrupted a task context kernel-mode FPU section and then a
softirqs were run at the end of that hardirq, those softirqs could not
use kernel-mode FPU.  This has now been fixed.  In combination with the
fact that the skcipher and aead APIs only support task and softirq
contexts, these can now just use kernel-mode FPU unconditionally on x86.

This simplifies the code and improves performance.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>