Revert "Documentation: devicetree: dwc2: Deprecate g-tx-fifo-size"

This binding was deprecated due to commit aa381a72 ("usb: dwc2:
gadget: fix TX FIFO size and address initialization"). However that
commit is now reverted, so also revert this commit.

The binding is valid and shouldn't be deprecated.

This reverts commit 65e1ff7f ("Documentation: devicetree: dwc2:
Deprecate g-tx-fifo-size").

Signed-off-by: John Youn <johnyoun@synopsys.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>