nouveau: find the smallest page allocation to cover a buffer alloc.

With the new uapi we don't have the comp flags on the allocation,
so we shouldn't be using the first size that works, we should be
iterating until we get the correct one.

This reduces allocations from 2MB to 64k in lots of places.

Fixes dEQP-VK.memory.allocation.basic.size_8KiB.forward.count_4000
on my ampere/gsp system.

Cc: stable@vger.kernel.org # v6.6
Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230811031520.248341-1-airlied@gmail.com