usb: phy: samsung: Introducing usb phy driver for hsotg

This driver uses usb_phy interface to interact with s3c-hsotg. Supports
phy_init and phy_shutdown functions to enable/disable usb phy. Support
will be extended to host controllers and more Samsung SoCs.

Signed-off-by: Praveen Paneri <p.paneri@samsung.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>