usb: phy: samsung: Add host phy support to samsung-phy driver

This patch adds host phy support to samsung-usbphy driver and
further adds support for samsung's exynos5250 usb-phy.

Signed-off-by: Praveen Paneri <p.paneri@samsung.com>
Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>