turnip: vsc improvements

turnip: vsc improvements

* Remove scratch_bo from cmdbuffer, use a device-global bo instead, which
  also includes border color (and eventually shaders for 3D blit path)
* Use CP_SET_BIN_DATA5_OFFSET to allow setting VSC buffer addresses only
  once at the start of the cmdstream
* Use scratch bo mechanism for a resizable VSC buffer
* Use feedback from "vsc_draw_overflow" and "vsc_prim_overflow" values to
  increase the size of VSC buffer when beginning to record a new cmdbuffer

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5570>