ipq806x: activate ATAG DTB mangle and EA8500 rootblock in dts

ipq806x: activate ATAG DTB mangle and EA8500 rootblock in dts

The command-line arguments provided by the boot loader will be
appended to a new device tree property: bootloader-args.
If there is a property "append-rootblock" in DT under /chosen
and a root= option in bootloaders command line it will be parsed
and added to DT bootargs with the form: <append-rootblock>XX.
Only command line ATAG will be processed, the rest of the ATAGs
sent by bootloader will be ignored.
This is usefull in dual boot systems, to get the current root partition
without afecting the rest of the system.

Signed-off-by: Adrian Panella <ianchi74@outlook.com>