panfrost: Implement glProvokingVertex() on Valhall
Starting with Valhall, the provoking vertex state is specified per-framebuffer
(batch) instead of per-draw. We use the pan_tristate infrastructure to translate
between desktop OpenGL's per-draw semantics to Valhall's per-framebuffer
semantic. This is notably not required for GLES or Vulkan.
Fixes arb-provoking-vertex-render on Valhall.
Note to reviewers: I split out the assert in the last patch from the active patch here. This is just to avoid the is_defined helper needing a backport.
Edited by Alyssa Rosenzweig