mfd: altr_a10sr: Add Altera Arria10 DevKit System Resource Chip

Add support for the Altera Arria10 Development Kit System Resource
chip which is implemented using a MAX5 as a external gpio extender
with the regmap framework over a SPI bus.

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>