Add runtime pm support to dynamically manage the clock to avoid enable/disable
clock in frequently that can improve the i2c bus transfer performance.

And use pm_runtime_force_suspend/resume() instead of lpi2c_imx_suspend/resume().
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>