Currently, vc4 has its own debugfs infrastructure that adds the debugfs
files on drm_dev_register(). With the introduction of the new debugfs,
functions, replace the vc4 debugfs structure with the DRM debugfs
device-centered function, drm_debugfs_add_file().

Moreover, remove the explicit error handling of debugfs related functions,
considering that the only failure mode is -ENOMEM and also that error
handling is not recommended for debugfs functions, as pointed out in [1].

[1] https://lore.kernel.org/all/YWAmZdRwnAt6wh9B@kroah.com/Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20221219120621.15086-5-mcanal@igalia.com