drm_fourcc.h should be picked up via the pkgconfig include, not the
system includedir directly.
Also consolidate the libdrm usage in va and msdk.
All this allows it to be picked up consistently (via the subproject,
for example).
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6932>
Modify the fix_output_format in vpp to directly generate caps with
negotiated src caps, and we have the correct dma caps negotiation in
fix_output_format function. And thus, we can remove the redundant
negotiation of using function pad_accept_memory in vpp.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5845>
