[MR] etnaviv: add low level ISA library

[Christian Gmeiner]

This MR adds a low level ISA library containing APIs for asm, diasm
and meta information. One benefit of moving all this stuff out of the
gallium driver is that it opens the door for vulkan. Unit tests are
included and the current etnaviv disasm gets replaced with the new
one.

https://gitlab.freedesktop.org/mesa/mesa/merge_requests/848
-- 
greets
--
Christian Gmeiner, MSc

https://christian-gmeiner.info