phy: exynos5-usbdrd: Add facility for VBUS-BOOST-5V supply

Some Exynos boards have a separate regulator controlling a
Boost 5V supply which goes as input for VBUS regulator.
So adding a control for the same in driver, to enable
vbus supply on the port.

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>