vc4: Rewrite the kernel ABI to support texture uniform relocation.

vc4: Rewrite the kernel ABI to support texture uniform relocation.

This required building a shader parser that would walk the program to find
where the texturing-related uniforms are in the uniforms stream.

Note that as of this commit, a new kernel is required for rendering on
actual VC4 hardware (currently that commit is named "drm/vc4: Introduce
shader validation and better command stream validation.", but is likely to
be squashed as part of an eventual merge of the kernel driver).