dt-bindings: usb: dwc3: Deprecate snps,ref-clock-period-ns

dt-bindings: usb: dwc3: Deprecate snps,ref-clock-period-ns

This property is redundant because we can determine the correct value for
REFCLKPER based on the "ref" clock. Deprecate it, and encourage users to
provide a clock instead. This also restricts the minimum and maximum to the
values documented in the register reference [1].

[1] https://www.xilinx.com/html_docs/registers/ug1087/usb3_xhci___guctl.html

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20220127200636.1456175-2-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>