arm: mvebu: turris_mox: Find DT nodes by compatible or alias instead of path

It is better to find DT nodes by compatible strings or aliases instead
of path.

There were issues with Linux some DTBs having different names of some
nodes, e.g.
  internal-regs
instead of
  internal-regs@d0000000

This should be a generic fix for such issues.

Also since fdt_support now contains needed functions, we can drop our
own implementations.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>