freedreno: Avoid wasting const buf space on unused UBO ranges.
We were doing just one upload range per UBO, extending as necessary to cover. By avoiding gaps, we get:
total instructions in shared programs: 9266114 -> 9255092 (-0.12%)
total full in shared programs: 343162 -> 341709 (-0.42%)
total constlen in shared programs: 1454368 -> 1275236 (-12.32%)
total cat6 in shared programs: 93073 -> 82589 (-11.26%)
total (ss) in shared programs: 212402 -> 206404 (-2.82%)
total (sy) in shared programs: 122905 -> 114007 (-7.24%)