imx-drm: imx-hdmi: convert HDMI clock settings to tabular form

Rather than having large if() and switch() statements, provide a table
to look up the register settings for various clock rates.

Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>