drm: do not set fb_info->pixmap fields

The drm drivers set the fb_info->pixmap fields without setting
fb_info->pixmap.addr. If this is not set the fb core will overwrite
these all fb_info->pixmap fields anyway, so there is not much point
in setting them in the first place.

[airlied: dropped nvidiafb piece - not mine]

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>