drm/drm_of: add drm_of_panel_bridge_remove function

This function is the pendant of drm_of_find_panel_or_bridge()
to remove a previously allocated panel_bridge.
Given a specific port and endpoint it remove the panel bridge.
Since drm_panel_bridge_remove() will check that bridge parameter
is not NULL and is a real drm_panel_bridge and no a simple bridge
it is safe to call it directly.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Tested-by: Philippe Cornu <philippe.cornu@st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1506936888-23844-3-git-send-email-benjamin.gaignard@linaro.org