radeonsi: Fix compute copies for subsampled formats.

radeonsi: Fix compute copies for subsampled formats.

We cannot do image stores (or render) to subsampled formats.

Reinterpret as R32_UINT instead.

si_set_shader_image_desc already uses the blockwidth from
the view formats, so the image width adjustments are
already implemented.

This is still icky with mipmapping on GFX9+ though, but
since it is mostly a video format I don't think that will
be much of an issue and broken mipmapping is still better
than broken everything.

Fixes: e5167a9276d "radeonsi: disable SDMA on gfx8 to fix corruption on RX 580"
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2535
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3853>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3853>