usb: dwc3: exynos: remove non-DT support for Exynos Specific Glue layer

DWC3 Exynos Specific Glue layer can be used only for Exynos SoCs.
In addition, non-DT for EXYNOS SoCs is not supported from v3.11;
thus, there is no need to support non-DT for DWC3 Exynos Specific
Glue layer.

The 'linux/platform_data/dwc3-exynos.h' file has been used for
non-DT support. Thus, the 'dwc3-exynos.h' file is removed, because
it is not used anymore.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>