Exynos5420 has different registers with other exynos5 SoCs to control
usb device phy, so need separated function to enable exynos5420 usb
device phy.
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>