drm/drm_of: Move drm_of_panel_bridge_remove_function into header.

drm/drm_of: Move drm_of_panel_bridge_remove_function into header.

Core drm shouldn't depend on anything in drm-kms-helper, or the drm
module will fail to load.

insmod drm fails with
[ 6087.674390] drm: Unknown symbol drm_panel_bridge_remove (err 0)

which is defined in drm_kms_helper.ko

This call was added by commit c70087e8f16f ("drm/drm_of: add
drm_of_panel_bridge_remove function"), and the fix is defining it in the
drm_of.h header, to break the circular dependency.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/8f95e623-9480-97dc-2414-77086d8aa49d@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@intel.com> #irc
Fixes: c70087e8f16f ("drm/drm_of: add drm_of_panel_bridge_remove function")
Acked-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>