This patch adds an example for I2C callbacks that is very similar to
the i2c-LSM9DS0 example except that it uses a PWM device that is built
into the platform.
This patch revises the I2C and GPIO initialization code to always be
run during platform boot rather than within each process that requires
it.
This patch also revises the gpio-output example to use a pin that is
set as an output by the default pinmux configuration. Previously, it
used a pin that was set as an output by the pinmux configuration that
is in effect when the OS does not change the pinmux configuration.