board/BuR: drop devicetree loading and lcd setup for linux-targets

board/BuR: drop devicetree loading and lcd setup for linux-targets

This patch  drops the lcd-screen setup, the summary screen and getting
mac-addresses based on a previous loaded device-tree for linux targets.
Selecting those linux target is simple, since we have only the brppt1.

In detail we do:
- drop the common lcd-setup code which relys on a fdt_blob
- drop the common dtb loading mechanism
- drop the now obsolete CONFIG_USE_FDT from board header and whitelist.

Signed-off-by: Hannes Schmelzer <oe5hpm@oevsv.at>