mesa: rework ParameterList to allow packing

mesa: rework ParameterList to allow packing

Currently everything is padded to 4 components. Making the list
more flexible will allow us to do uniform packing.

V2 (suggestions from Nicolai):
- always pass existing calls to _mesa_add_parameter() true for padd_and_align
- fix bindless param value offsets
- remove left over wip logic from pad and align code
- zero out param value padding
- whitespace fix

Reviewed-by: Marek Olšák <marek.olsak@amd.com>