i2c: s3c2410: Handle i2c sys_cfg register in i2c driver

Let's handle i2c interrupt re-configuration in i2c driver. This will
help us in removing some soc specific checks from machine files and
will help in removing static iomapping of SYS register in exynos.c

Also handle saving and restoring of SYS_I2C_CFG register during
suspend and resume of i2c driver.

Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>