Features
   * AES performance improvements. Uplift varies by platform,
     toolchain, optimisation flags and mode.
     Aarch64, gcc -Os and CCM, GCM and XTS benefit the most.
     On Aarch64, uplift is typically around 20 - 110%.
     When compiling with gcc -Os on Aarch64, AES-XTS improves
     by 4.5x.
