radeonsi: move BCOLOR PS input locations after all other inputs

radeonsi: move BCOLOR PS input locations after all other inputs

BCOLOR inputs were immediately after COLOR inputs. Thus, all following inputs
were offset by 1 if color_two_side was enabled, and not offset if it was not
enabled, which is a variation that's problematic if we want to have 1 variant
per shader and the variant doesn't care about color_two_side (that should be
handled by other bytecode attached at the beginning).

Instead, move BCOLOR inputs after all other inputs, so BCOLOR0 is at location
"num_inputs" if it's present. BCOLOR1 is next.

This also allows removing si_shader::nparam and
si_shader::ps_input_param_offset, which are useless now.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>