crypto: x86/aegis128 - eliminate some indirect calls

Instead of using a struct of function pointers to decide whether to call
the encryption or decryption assembly functions, use a conditional
branch on a bool.  Force-inline the functions to avoid actually
generating the branch.  This improves performance slightly since
indirect calls are slow.  Remove the now-unnecessary CFI stubs.

Note that just force-inlining the existing functions might cause the
compiler to optimize out the indirect branches, but that would not be a
reliable way to do it and the CFI stubs would still be required.

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