i2c: at91: add support for advanced digital filtering

Add new platform data support for advanced digital filtering for i2c.
The sama5d2 and sam9x60 support this feature.
This digital filter allows the user to configure the maximum
width of the spikes that can be filtered.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>