ARM: EXYNOS: Setup legacy i2c controller interrupts

On Exynos5 we have a new high-speed i2c controller. The interrupt
sources for the legacy and new controller are muxed and are controlled
via the SYSCON I2C_CFG register. At reset the interrupt source is
configured for the high-speed controller, to continue using the old
i2c controller we need to modify the I2C_CFG register.

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