i2c: S3C24X0: Finish Kconfig migration

i2c: S3C24X0: Finish Kconfig migration

Finish moving this driver to Kconfig.
- Update the dependency logic for Exynos5 too
- Remove the unused CONFIG_SYS_I2C_S3C24X0_SPEED variable
- Drop CONFIG_SYS_I2C_S3C24X0_SLAVE as it's always set to 0.
- Move the internal SYS_I2C_S3C24X0_SLAVE define closer to the only user.

Cc: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>