Add support for the Ethernut 5 open hardware design, based
on Atmel's AT91SAM9XE512 SoC.

V4
 - Fix several coding style issues.
 - Move machine type to config file.
 - Remove use of CONFIG_ATMEL_LEGACY.
Signed-off-by: NTim Schendekehl <tim.schendekehl@egnite.de>