radv: Add suballocation for shaders.

radv: Add suballocation for shaders.

This reduces the number of BOs that we need for the BO lists during
a submission.

Currently uses a fairly simple linear search for finding free space,
that could eventually be improved to a binary tree, which with some
per-node info could make a check for space O(1) and finding it O(log n),
in the number of buffers in that slab.

Signed-off-by: Bas Nieuwenhuizen <basni@google.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>