ARM: at91: Remove the support for the RSI EWS board

The platform is end of life/support and should not clutter
the mach-at91 directory with non-DT files. It is therefore
removed.

Signed-off-by: Josef Holzmayr <holzmayr@rsi-elektrotechnik.de>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>