pvr: Remove some magic numbers and increments from km stream

pvr: Remove some magic numbers and increments from km stream

 - Update and add csbgen definitions to make the content of the
   geom and frag km stream more obvious.

 - Replace some of the hard coded constants with defines.

 - Adds some static assert to make the provenance of definitions
   more clear as well as making sure things fit properly.

Signed-off-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24138>