i2c: omap: Add calls for pinctrl state select

This adds calls to pinctrl subsystem in order to switch pin states
on suspend/resume if you provide a "sleep" state in DT.

If no "sleep" state is provided in the DT, these calls turn
to NOPs, so we don't need error checking here.

Signed-off-by: Pascal Huerst <pascal.huerst@gmail.com>
Reviewed-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>