drm: imx: imx-hdmi: move imx-hdmi to bridge/dw_hdmi

the original imx hdmi driver is under drm/imx/,
which depends on imx-drm, so move the imx hdmi
driver out to drm/bridge and rename it to dw_hdmi

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>