There is some special-casing needed in a competent back-end.  However, they
can do their special-casing easily enough based on whether or not the
offset is a constant.  In the mean time, having the *_indirect variants
adds special cases a number of places where they don't need to be and, in
general, only complicates things.  To complicate matters, NIR had no way to
convdert an indirect load/store to a direct one in the case that the
indirect was a constant so we would still not really get what the back-ends
wanted.  The best solution seems to be to get rid of the *_indirect
variants entirely.

This commit is a bunch of different changes squashed together:

 - nir: Get rid of *_indirect variants of input/output load/store intrinsics
 - nir/glsl: Stop handling UBO/SSBO load/stores differently depending on indirect
 - nir/lower_io: Get rid of load/store_foo_indirect
 - i965/fs: Get rid of load/store_foo_indirect
 - i965/vec4: Get rid of load/store_foo_indirect
 - tgsi_to_nir: Get rid of load/store_foo_indirect
 - ir3/nir: Use the new unified io intrinsics
 - vc4: Do all uniform loads with byte offsets
 - vc4/nir: Use the new unified io intrinsics
 - vc4: Fix load_user_clip_plane crash
 - vc4: add missing src for store outputs
 - vc4: Fix state uniforms
 - nir/lower_clip: Update to the new load/store intrinsics
 - nir/lower_two_sided_color: Update to the new load intrinsic

NIR and i965 changes are

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

NIR indirect declarations and vc4 changes are

Reviewed-by: Eric Anholt <eric@anholt.net>

ir3 changes are

Reviewed-by: Rob Clark <robdclark@gmail.com>

NIR changes are

Acked-by: Rob Clark <robdclark@gmail.com>