ARM: dts: imx28-evk: Convert to the new display bindings

imx28-evk board has a Seiko 43WVF1G parallel display.

Instead of hardcoding the display timings in the device tree, use
the "sii,43wvf1g" compatible instead.

This aligns with the new mxsfb bindings scheme documented at:
Documentation/devicetree/bindings/display/mxsfb.txt

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>