ARM: dts: imx7-colibri: multiple node updates

1. Move u-boot specific nodes to u-boot dts include: legacy lcdif
node and aliases.
2. Add iomux configuration for LCD.
3. Drop un-needed u-boot,dm-pre-reloc for alias node.
4. Fix display-timings, use the one from Toradex downstream kernel [1]

[1]: https://git.toradex.com/cgit/linux-toradex.git/tree/arch/arm/boot/dts/imx7-colibri-eval-v3.dtsi?h=toradex_4.9-2.3.x-imx#n206


Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>