usb: dwc3: exynos: Remove dead code

All supported Exynos variants provide respective generic PHY framework
based drivers for controlling USB PHYs, so there is no point
creating fake USB PHYs based on platform devices. While removing useless
code, remove calls to runtime PM, which have no effect.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>