clk: imx51: propagate rate across ipu_di*_sel

This propagates rate requests from the display interface to the divider
or PLL output, allowing to hit the required display rate in many more
cases.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-By: Wladimir J. van der Laan <laanwj@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>