crypto: aesni - replace function pointers with static branches

Replace the function pointers in the GCM implementation with static branches,
which are based on code patching, which occurs only at module load time.
This avoids the severe performance penalty caused by the use of retpolines.

In order to retain the ability to switch between different versions of the
implementation based on the input size on cores that support AVX and AVX2,
use static branches instead of static calls.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>