kms_plane: Add panning test for primary plane

kms_plane: Add panning test for primary plane

Get CRCs of a full red and a full blue surface as reference.

Create a big framebuffer that is twice width and twice height as the
current display mode.

Fill the top left quarter with red, bottom right quarter with blue
Check the scanned out image with the CRTC at position (0, 0) of the
framebuffer and it should be the same CRC as the full red fb
Check the scanned out image with the CRTC at position (hdisplay,
vdisplay) and it should be the same CRC as the full blue fb

v2: Fix a few things here and there (Damien)

Cc: Lei Liu <lei.a.liu@intel.com>
Cc: Yi Sun <yi.sun@intel.com>
Signed-off-by: Lei Liu <lei.a.liu@intel.com>
Signed-off-by: Yi Sun <yi.sun@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>