cgd and aes instruction set

[Alexander Nasonov <alnsn%yandex.ru@localhost>]

Hi,

I'd like to bring up two things on this list. The first one is
trivial, the second will take some time to implement but it should
be pretty straightforward.

1. cgd isn't enabled in GENERIC64. Given a recent progress on getting
   aarch64 support on cloud platforms (Scaleway & AWS clouds, for
   instance), disk encryption should be readily available for people
   who don't want to leave valuable information on someone else's
   disks.
2. Our current impementation is a bit slow and it's not constant-time.
   I'd like to work on improving it. Crypto code itself is
   straightforward but it uses simd registers (or vfp, I'm not very
   sure on the terminology), and they should be saved/restored.
   ryo@ pointed me out at matt@'s work in cpu_in_csum_neon.c but
   it's for arm32 and it's incomplete. Is there anything similar
   for aarch64?

-- 
Alex