crypto: arm/aes-ce - build for v8 architecture explicitly

The NEON/Crypto Extensions based AES implementation for 32-bit ARM
can be built in a kernel that targets ARMv6 CPUs and higher, even
though the actual code will not be able to run on that generation,
but it allows for a portable image to be generated that can will
use the special instructions only when they are available.

Since those instructions are part of a FPU profile rather than a
CPU profile, we don't override the architecture in the assembler
code, and most of the scalar code is simple enough to be ARMv6
compatible. However, that changes with commit c61b1607

,
which introduces calls to the movw/movt instructions, which are
v7+ only.

So override the architecture in the .S file to armv8-a, which
matches the architecture specification in the crypto-neon-fp-armv8
FPU specificier that we already using. Note that using armv7-a
here may trigger an issue with the upcoming Clang 10 release,
which no longer permits .arch/.fpu combinations it views as
incompatible.

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: c61b1607

 ("crypto: arm/aes-ce - implement ciphertext stealing ...")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>