multimedia/mpv: track VDPAU dependency on X11

Checking for VDPAU acceleration : x11 not found
Checking for VDPAU with OpenGL/X11 : vdpau not found

PR: 267816
Reported by: amdmi3

(cherry picked from commit 223e207711169c0780ad0a27e479eafb4c27f63c)