greybus: i2c-gb: add missing header for 3.14 build

The 3.14 kernel cannot build the module properly without
these includes.

Remove as well some irqchip methods that were introduced
in recent 3.17+ kernel.

Signed-off-by: Benoit Cousson <bcousson@baylibre.com>
Acked-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>