PIPE_CAP_PACKED_UNIFORMS conflates several things: Lowering uniforms i/o
at the st level instead of the backend, packing uniforms with no padding
at all, and lowering to UBOs.

Requiring backends to lower uniforms i/o for !PIPE_CAP_PACKED_UNIFORMS
leads to the driver needing to either link against the type size function
in mesa/st, or duplicating it in the backend.  Given that all backends
want this lower-io as far as I can tell, just move it to mesa/st to
resolve the link issue and avoid the driver author needing to understand
st's uniforms layout.

Incidentally, fixes uniform layout failures in nouveau in:

dEQP-GLES2.functional.shaders.struct.uniform.sampler_nested_fragment
dEQP-GLES2.functional.shaders.struct.uniform.sampler_nested_vertex
dEQP-GLES2.functional.shaders.struct.uniform.sampler_array_fragment
dEQP-GLES2.functional.shaders.struct.uniform.sampler_array_vertex

and I think in Lima as well.

v2: fix indents

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