usb:hsotg:samsung: Wrappers for USB PHY methods

Wrappers for PHY methods have been added for readability and reduction
of code repetition.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>