arm: mxs: Add LCDIF clock configuration function

This function turns on the LCDIF clock and configures it's frequency. The
dividers settings are calculated within the function and the current
implementation should be fast and accurate.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Stefano Babic <sbabic@denx.de>