Currently it is not possible to use HDMI and LVDS at the same time on a
imx6dl-sabresd board.

Fix this usecase by setting IMX6QDL_CLK_PLL3_PFD1_540M to 540MHz and
also by setting it as the parent of IMX6QDL_CLK_IPU1_SEL.

Based on the configuration done in the FSL kernel.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>