drm: renesas: shmobile: Atomic conversion part 1

Implement atomic mode setting for both the primary and overlay planes.
This involves:
  - Moving the primary plane handling code from CRTC mode setting to
    plane handling shared by primary and overlay planes,
  - Adding basic CRTC and mode config atomic mode setting ops, which
    don't do much yet.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/a6b698a1c8c1eaf631c2f928f5888ab5fe7aa4c3.1694767209.git.geert+renesas@glider.be