update apalis-imx6 documentation

Number of changes are done to the apalis-imx6 image that need to be documented.

• u-boot now defaults to ixora v1.1 dtb, using any other carrier board need to change the fdt_file variable in uboot environment.
• ixora v1.1 dtb enables the new capasitive touch display (https://www.toradex.com/accessories/capacitive-touch-display), using Fusion displays requires change to kernel and possible to the u-boot.