dri3: Fix dri3_buffers_from_pixmap request.

Sending pixmap depth and bpp was omitted, so the Mesa
X11 + EGL + DRI3 side of things always failed to
dri3_create_image_khr_pixmap_from_buffers(), which led
to failure of X11 + EGL compositing under DRI3 under,
e.g., KDE Plasma 5.

Fixes: 6e7c40f6 ("dri3: Add multi-planar/modifier buffer requests")
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Reviewed-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Tested-by: Mike Lothian <mike@fireburn.co.uk>