ARM: EXYNOS: Fix i2c suspend/resume for legacy controller

On resuming from suspend the i2c configuration register that is part
of system controller resets to 0xf. This sets the interrupt source to
the new high speed i2c rather than the legacy one that we are using.
Save and restore the I2C_CFG register for exynos5 to fix this.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>