radeonsi: Copy all planes with multi-plane staging textures

radeonsi: Copy all planes with multi-plane staging textures

Multi-plane format textures are allocated as a single buffer
for all planes, so when mapping first plane it will map
all planes.
However, when staging texture is used, only the first
plane will be available.

When asked to map first plane of multi-plane texture,
create a staging texture with matching multi-plane format
and copy all planes on map/unmap.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24389>