clk: imx: vf610: add TCON ipg clock

Add the ipg (bus) clock for the TCON modules (Timing Controller). This
module is required by the new DCU DRM driver, since the display signals
pass through TCON.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>