etnaviv: implement UBOs

etnaviv: implement UBOs

At the same time, use pre-HALTI2 to use address register for indirect
uniform loads, since integers/LOAD instruction isn't always available.

Passes all dEQP-GLES3.functional.ubo.* on GC7000L. GC3000 with an extra
flush hack passes most of them, but still fails on some of the cases with
many loads.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3389>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3389>