I2C: OMAP2+: Introduce I2C IP versioning constants

These represent the two kinds of (incompatible) OMAP I2C
peripheral unit in use so far.

The constants are in linux/i2c-omap.h so the omap i2c driver can have
them too.

Cc: patches@linaro.org
Cc: Ben Dooks <ben-linux@fluff.org>
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andy Green <andy.green@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>