doc: DTS: Update DWC3 binding to provide reference to generic bindings
doc: DTS: Update DWC3 binding to provide reference to generic bindings

Since the Synopsys DWC3 controller driver inherits the generic bindings
defined in 'usb/generic.txt', this patch tries to capture the same in
the DWC3 binging documentation to avoid any confusion in usage of properties
like 'dr_mode' for certain SoCs like FSL LS2080A.

Signed-off-by: Bhupesh Sharma <4ea540b5fc8347f73706cff6303216b2e0bede0b@freescale.com>
Signed-off-by: Arnd Bergmann <f2c659f01951776204a6c5b902787d9019fbeebd@arndb.de>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs