freedreno/a6xx: Rework border-color handling

Rob Clark requested to merge robclark/mesa:fd/bcolor-rework into main

Delete code, fix things, go faster. On top of !19560 (closed)

Replaces draw-time bcolor table construction (which only took into account VS and FS) with a global bcolor table. This more or less matches what zink+tu end up doing, but with a bit of cleverness to re-use table entries instead of constantly appending new ones. This moves all of the overhead out of draw-time and into CSO creation time.

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