drm: renesas: shmobile: Remove internal CRTC state tracking

Now the suspend/resume methods no longer need to look at internal driver
state, the dpms and started fields in the shmob_drm_crtc structure can
be removed, as well as the shmob_drm_crtc_dpms() wrapper.  After this,
shmob_drm_crtc_atomic_{en,dis}able() became just wrappers around
shmob_drm_crtc_st{art,op}(), so inline the latter.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/905b9ca72f43d40438c8cb1199cde140eb123204.1694767209.git.geert+renesas@glider.be