Fix the following sparse warning:

drivers/usb/phy/phy-samsung-usb2.c:50:26: sparse: incorrect type in argument 1 (different address spaces)
drivers/usb/phy/phy-samsung-usb2.c:50:26:    expected void const volatile [noderef] <asn:2>*addr
drivers/usb/phy/phy-samsung-usb2.c:50:26:    got void *

Cc: Vivek Gautam <gautam.vivek@samsung.com>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

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>