radv/amdgpu: Rewrite fallback code path so it can split submissions.

radv/amdgpu: Rewrite fallback code path so it can split submissions.

Currently, radv_queue already splits submissions but we want to
change this and be able to split them in the winsys code as well.
Necessary because we want to split based on number of actual
IBs not number of command buffers, but radv_queue is not
aware of IBs.

Note that this commit does not actually take this new split into
use yet, that will be done in a following commit when it is ready,
this is why we set the max IB count higher than radv_queue here.

This commit is the first step in making "fallback" the default and
only submission code path.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22354>