i2c/gpio: add DT support

To achieve DT support, we need to populate a custom platform_data in a
private struct from DT information. To simplify code, the adapter and
algorithm are also put into the private struct.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>