stats: i2c: I2C stats

Adds the ability for I2C drivers to report synchronous transfer stats
using a I2C specific macro to define the device instance.

The macro creates a container for device_state which allows for per
instance device class common data structure to be used in the device
class api (ex: i2c.h). This is used to maintain per driver instance
stats for all i2c drivers. This is a reusable idea across other device
classes as desired.

Using Kconfig device class stats may be turned on/off individually
this way as well, in this case I2C_STATS.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>