Moving register and structure definitions to header file,
and keeping the generic functions to be used across
multiple PHYs in common phy helper driver under SAMSUNG_USBPHY,
and moving USB 2.0 PHY driver under SAMSUNG_USB2PHY.

Also allowing samsung PHY drivers be built as modules.
Signed-off-by: NVivek Gautam <gautam.vivek@samsung.com>
Acked-by: NKukjin Kim <kgene.kim@samsung.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>