crypto: aegis128/simd - build 32-bit ARM for v8 architecture explicitly

Now that the Clang compiler has taken it upon itself to police the
compiler command line, and reject combinations for arguments it views
as incompatible, the AEGIS128 no longer builds correctly, and errors
out like this:

  clang-10: warning: ignoring extension 'crypto' because the 'armv7-a'
  architecture does not support it [-Winvalid-command-line-argument]

So let's switch to armv8-a instead, which matches the crypto-neon-fp-armv8
FPU profile we specify. Since neither were actually supported by GCC
versions before 4.8, let's tighten the Kconfig dependencies as well so
we won't run into errors when building with an ancient compiler.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reported-by:  <ci_notify@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>