usb: dwc3: exynos: remove platform data support

We are removing plat data which was used till now to init and
exit phy. We no longer need this since dwc3-core takes care of
initializing and shutting-down the phy using usb_phy_init()
and usb_phy_shutdown().

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>