gallium: ddebug: Add missing fence related wrappers

gallium: ddebug: Add missing fence related wrappers

Without that `GALLIUM_DDEBUG=always kmscube -A` would segfault like

  #0  0x0000000000000000 in  ()
  #1  0x0000ffffa72a3c54 in dri2_get_fence_fd (_screen=0xaaaaed4f2090, _fence=0xaaaaed9ef880) at ../src/gallium/state_trackers/dri/dri_helpers.c:140
  #2  0x0000ffffa8744824 in dri2_dup_native_fence_fd (drv=0xaaaaed5010c0, disp=0xaaaaed5029a0, sync=0xaaaaed9ef7c0) at ../src/egl/drivers/dri2/egl_dri2.c:3050
  #3  0x0000ffffa87339b8 in eglDupNativeFenceFDANDROID (dpy=0xaaaaed5029a0, sync=0xaaaaed9ef7c0) at ../src/egl/main/eglapi.c:2107
  #4  0x0000aaaabd29ca90 in  ()
  #5  0x0000aaaabd401000 in  ()

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>