usb:hsotg:samsung: Comments reorganization and cleanup

Refactor all comments to comply with kernel codding style.
Moreover doxygen descriptions have been added for selected functions.
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>