x86/64: enable AES-NI support in kernel

The kernel will detect if the host supports this, so we can just enable
it in the kernel config.

Tested on an APU2 with AES-NI support and a KVM VM on a Xeon E5520 host
without AES-NI support.

Throughput over an IPsec tunnel between these 2 hosts increased from
~63Mbps to ~140Mbps. Ciphers: AES_GCM_16_256/PRF_HMAC_SHA2_512/ECP_521.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>