This patch adds the gpio.c and gpio.h files, which support
access to GPIO Controller (non-legacy) configuration register
through a function interface.
It doesn't add interrupt support due to pinmux reasons. On
Galileo Gen 2 we need to configure a pin as input/interrupt
using pinmux and this can only be achieved through I2C. There's
one pin exported by default as GPIO output and we used this one
to test this driver.
In the future, we plan to add an I2C driver and a pinmux configuration
driver in order to solve this kind of problems.
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