radeonsi: implement fw based mcbp

radeonsi: implement fw based mcbp

Some chips support firmware based mcbp. If supported this means
radeonsi needs to allocate 3 buffers and pass them to the firmware.

From there, the firmware will handle mcbp and register shadowing
on its own so we don't need to insert LOAD packet in the preamble.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21986>