usb: dwc3: Add a check for the DWC_usb3 core

Add a helper function to check if we are running on a DWC_usb3 core.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Change-Id: Ic0c3810b798df8bf34a2ad7e1879884e7bf3c8f5
Git-commit: a987a906e95c4d80a364629d6bcb7cf69d2018e4
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[mrana@codeaurora.org: resolved merge conflicts]
Signed-off-by: Mayank Rana <mrana@codeaurora.org>