turnip: Move remaining drm code to tu_drm.c

turnip: Move remaining drm code to tu_drm.c

This moves the semaphore implementation and tu_QueueSubmit to
tu_drm.c, such that that's the only file including xf86drm.h and
msm_drm.h.  This way, the entire kernel interface is contained in
tu_drm.c

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5999>