crypto: morus - Mark MORUS SIMD glue as x86-specific

Commit 56e8e57f ("crypto: morus - Add common SIMD glue code for
MORUS") accidetally consiedered the glue code to be usable by different
architectures, but it seems to be only usable on x86.

This patch moves it under arch/x86/crypto and adds 'depends on X86' to
the Kconfig options and also removes the prompt to hide these internal
options from the user.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Ondrej Mosnacek <omosnacek@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>