crypto: aesni - fix build on x86 (32bit)

It seems commit d764593a "crypto: aesni - AVX and AVX2 version of AESNI-GCM
encode and decode" breaks a build on x86_32 since it's designed only for
x86_64. This patch makes a compilation unit conditional to CONFIG_64BIT and
functions usage to CONFIG_X86_64.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>