I2C: Support default only pinctrl state.

In some cases, only default option is needed for i2c devices. This is to
remove the requirement for "on_i2c" and "off_i2c" states.

Bug: 169270302
Signed-off-by: Edmond Chung <edmondchung@google.com>
Change-Id: I4902f98799833365a217b5fb3c159220510e7804
(cherry picked from commit 6bafd4fa86ac1099b583d432fec50ccb9d04e629)