drm: omapdrm: Move crtc info out of the crtc structure

The crtc info structure is only used to setup the crtc through the DSS
API. Move it from the crtc structure to local variables in
omap_crtc_dss_enable().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>