drm/omap: Get rid of DRM_OMAP_NUM_CRTCS config option

Allocate one CRTC for each connected output and get rid of
DRM_OMAP_NUM_CRTCS config option. We still can not create more CRTCs
than we have DSS display managers. We also reserve one overlay per
CRTC for primary plane so we can not have more CRTCs than we have
overlays either.

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