arm, at91: add spi dataflash support for the taurus board

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Bo Shen <voice.shen@atmel.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>