i2c: s3c2410: Refactor ifdefs for PM_SLEEP

Use the PM_SLEEP ifdef for system suspend and resume. This is partly
in preparation for adding runtime operations and partly because a user
may in theory choose to enable runtime suspend but not system suspend.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>