Currently the HDMI splash screen image quality on mx6solo does not show a
very stable image.

By comparing the IPU driver from U-boot with the one from FSL 4.1.0 BSP,
we can see that there is an inverted logic for setting the DI_GEN_POL_CLK bit.

>From FSL BSP [1] we have:

	if (!sig.clk_pol)
		di_gen |= DI_GEN_POLARITY_DISP_CLK;

Applying the same logic into U-boot fixes the HDMI image stability.

[1] git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/tree/drivers/mxc/ipu3/ipu_disp.c?h=imx_3.0.35_4.1.0
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Tested-by: NEric Nelson <eric.nelson@boundarydevices.com>
Acked-by: NEric Nelson <eric.nelson@boundarydevices.com>
Acked-by: NStefano Babic <sbabic@denx.de>