usb: s3c-otg: Split out PHY control

usb: s3c-otg: Split out PHY control

Split the Samsung specific PHY control into a separate file
and compile this into the S3C OTG driver only if used on a
Samsung system.

Signed-off-by: Marek Vasut <[email protected]>
Cc: Chin Liang See <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Vince Bridgers <[email protected]>
Acked-by: Pavel Machek <[email protected]>
Cc: Stefan Roese <[email protected]>
Reviewed-by: Lukasz Majewski <[email protected]>
Tested-by: Lukasz Majewski <[email protected]>