i2c: omap: switch over to autosuspend API

this helps us reduce unnecessary pm transitions
in case we have another i2c message starting soon.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>