panfrost: Move pan_bo to root panfrost

panfrost: Move pan_bo to root panfrost

Now that its Gallium dependencies have been resolved, we can move this
all out to root. The only nontrivial change here is keeping the
pandecode calls in Gallium-panfrost to avoid creating a circular
dependency between encoder/decoder. This could be solved with a third
drm folder but this seems less intrusive for now and Roman would
probably appreciate if I went longer than 8 hours without breaking the
Android build.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4382>