anv: Move viewport/scissor emit to genX_cmd_buffer.c

anv: Move viewport/scissor emit to genX_cmd_buffer.c

There's never been a particularly good reason to stick these in gfx7/8.
We mostly did it to deduplicate the binary a bit but this shouldn't emit
all that much code.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14961>