drm/vc4: crtc: Move debugfs_name to crtc_data

All the CRTCs, including the TXP, have a debugfs file and name so we can
consolidate it into vc4_crtc_data.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>