drm/atomic: Remove WARN_ON for invalid plane configuration.

drm/atomic: Remove WARN_ON for invalid plane configuration.

Userspace can set a FB_ID on a plane without setting CRTC_ID, which
will fail with -EINVAL, but the kernel shouldn't warn about that.

Same for !FB_ID and CRTC_ID being set.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130102704.28016-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Harry Wentland <harry.wentland@amd.com>