i2c: davinci: Add PM Runtime Support

66AK2G has I2C instances that are not apart of the ALWAYS_ON power domain
unlike other Keystone 2 SoCs and OMAPL138. Therefore, pm_runtime
is required to insure the power domain used by the specific I2C instance is
properly turned on along with its functional clock.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>