usb: dwc3: Add GDBGLTSSM register offset for dwc31 IP

For DWC USB 3.1 IP, the register location for GDBGLTSSM has
moved to the link register block. Add the macro definition
for it. Revision checks needs to be added wherever the register
is read to ensure the correct offset is used.

Change-Id: I814914e51fa3a5534de93770d705728223f8d7f6
Signed-off-by: Jack Pham <jackp@codeaurora.org>