gpio.c: check that real gpio did initialise correctly

On platforms without muxing perform a little more checking when the 'real'
linux/sysfs gpio is opened. We don't expect this to fail but on platforms where
the linux gpios can be changed depending on pinctrl/bios configuration this
might not always be the case.

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
i2c: define i2c #5 correctly on minnowboard max (low speed header)

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>