dt-bindings: usb: uhci: Add reset property

The UHCI controller on Aspeed SoCs (including AST2700) requires
its reset line to be deasserted before the controller can be used.
Add an optional "resets" property to the UHCI device tree bindings
to describe the phandle to the reset controller.

This property is optional for platforms which do not require
explicit reset handling.

Signed-off-by: Ryan Chen <ryan_chen@aspeedtech.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20250922052045.2421480-2-ryan_chen@aspeedtech.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>