nir,ac/llvm: add nir_intrinsic_load_viewport_xy_scale_and_offset

Used by RADV/Radeonsi NGG culling. Pack them into a single vec4
load for radeonsi to reduce const buffer load.

Acked-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17651>
3 files changed