Since most of the DTS file names follow a common scheme now, let's
update the automatically generated DEVICE_DTS value and get rid
of some DEVICE_DTS and all BOARD_NAME entries for individual devices.
This should specifically make the job easier for developers adding
new devices, as they are not tempted to copy over BOARD_NAME anymore.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>