ARM: dts: add twi nodes for atmel SoCs

Add TWI nodes for atmel SoCs but keep i2c-gpio ones in order to let the
choice to the user in dts files.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>