drm/vkms: Compute CRC with Cursor Plane

This patch compute CRC for output frame with cursor and primary plane.
Blend cursor with primary plane and compute CRC on the resulted frame.

This currently passes cursor-size-change, and cursor-64x64-[onscreen,
offscreen, sliding, random, dpms, rapid-movement] from igt
kms_cursor_crc tests.

Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/b1749f5c90da5721a481f12740e2e370edb4a752.1536210181.git.hamohammed.sa@gmail.com