nv50/ir: add support for different sampler and resource index on nve4

nv50/ir: add support for different sampler and resource index on nve4

And remove non-working code for indirect sampler/resource selection.
Will be added back later.

Includes code from "nv50/ir/tgsi: Resource indirect indexing" by
Francisco Jerez (when mixing the R and S handles we can only specify
them via a register, i.e. indirectly, unless we upload all the used
handle combinations to c[] space, which we don't for now).