freedreno/ir3: re-work shader inputs/outputs

freedreno/ir3: re-work shader inputs/outputs

Allow inputs/outputs to be vecN (ie. whatever their actual size is), and
use split to get scalar components of inputs, and collect to gather up
scalar components of outputs.

The main motivation is to simplify RA, by only having to consider split/
collect to figure out where values need to land in consecutive scalar
registers, rather than having to also deal with left/right neighbors.

Because of varying packing, and the resulting fractional location
(location_frac), to implement load_input/store_output, it is still
convenient to have a table of scalar inputs/outputs.  We move this to
the compile ctx (since it is only needed for nir->ir3).

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Eric Anholt <eric@anholt.net>