ARM: i.MX6: ipu_di_sel clocks can set parent rates

To obtain exact pixel clocks, allow the DI clock selectors to influence
the PLLs that they are derived from.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>