drm/bridge: dumb-vga-dac: Rename internal symbols to simple-bridge

The dumb-vga-dac driver is a simple DRM bridge driver for simple VGA
DACs that don't require configuration. Other non-VGA bridges fall in a
similar category, and would benefit from a common driver. Prepare for
this by renaming the internal symbols from dumb-vga-dac to
simple-bridge.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226112514.12455-11-laurent.pinchart@ideasonboard.com