On XeHP, the XY_BLOCK_COPY_BLT command has a number of fields that
describe the layout of the surface, much like SURFACE_STATE does.
Several of them are encoded in such a similar manner that we really
would like to reuse the isl helpers for emitting those. This commit
moves them into a new isl_genX_helpers.h file which I can include
from the BLORP code. (The alternative would be to add XY_BLOCK_COPY_BLT
filling commands to isl, but that...seems more like a BLORP feature.)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14094>