ARM: EXYNOS4: Add support for secondary MMC port on ORIGEN

Secondary MMC port on ORIGEN is connected to sdhci instance 0.
Support for secondary MMC port is extended by registering
sdhci instance 0.

Since sdhci instance 2 can contain a bootable media, sdhci
instance 0 is registered after instance 2.

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
[kgene.kim@samsung.com: Added comments in registering sdhci]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>