drm/kmb: Disable change of plane parameters

Due to HW limitations, KMB cannot change height, width, or
pixel format after initial plane configuration.

v2: removed memset disp_cfg as it is already zero.

Fixes: 7f7b96a8

 ("drm/kmb: Add support for KeemBay Display")
Signed-off-by: Edmund Dea <edmund.j.dea@intel.com>
Signed-off-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211013233632.471892-4-anitha.chrisanthus@intel.com


Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>