drm/bridge: dumb-vga-dac: Rename driver to simple-bridge

The dumb-vga-dac driver can support simple DRM bridges without being
limited to VGA DACs. Rename it 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>
Acked-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/20200226112514.12455-12-laurent.pinchart@ideasonboard.com