[xserver] Add definitions for the AArch64 architecture

[Marcin Juszkiewicz]

Hi

As my work nowadays is getting as much as possible built for AArch64
platform I took some time to get "xserver-xorg" 1.13.1 built.

My first attempt was same as Thomas Petazzoni did. Xserver builds and
starts fine but graphical output is wrong:

https://plus.google.com/u/0/105007947798310229700/posts/grcK83g5jys

So I changed byte order from LSBFirst to MSBFirst and now it looks like
it should:

https://plus.google.com/u/0/105007947798310229700/posts/dRu2UVEv9gz

And I love how xf86EnableIO got cleaned - I had to patch them too.