Refactor looking for dtree_dev_t

The code is duplicated so it is desirable to
make it cleaner by 'extract function' step.
Move parsing functions upper in the source

We need at least parse_addr in some other place
where the function has not been accessible.
Allow specify base address instead of a device name

This allows to access devices that are not present in
the current device tree more easily.
Remove '\n\'
Allow ignoring of device-tree