freedreno/a6xx: Use LDC for UBO loads.

It saves addressing math, but may cause multiple loads to be done and
bcseled due to NIR not giving us good address alignment information
currently.  I don't have any workloads I know of using non-const-uploaded
UBOs, so I don't have perf numbers for it

This makes us match the GLES blob's behavior, and turnip (other than being
bindful).

Part-of: <mesa/mesa!4858>