drm: Don't include <linux/fb.h> in drm_crtc_helper.h

Including <linux/fb.h> in drm_crtc_helper.h is not required. Remove
the include statement and avoid rebuilding DRM whenever the fbdev
header changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20230111130206.29974-4-tzimmermann@suse.de