freedreno: handle GMEM height limits

Fixes an assert that was triggering with ffox webrenderer:

firefox: src/freedreno/registers/adreno/a6xx-pack.xml.h:15500: pack_A6XX_GRAS_BIN_CONTROL: Assertion `((fields.binh >> 4) & 0xffffff80) == 0' failed.

I've managed to confirm that we can go above 1024 for tile height.. seems like we might be able to go above 1024 for tile width (on a6xx). It's a bit tricky to come up with a scenario to find the exact upper limit (if there is another limit lower than bitfield sizes), but dropping WIP since this is at least an improvement.