dt-bindings: clock: add RMII clock selection

Add RMII clock selection for ENETC0 and ENETC1.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20240829011849.364987-3-wei.fang@nxp.com


Signed-off-by: Abel Vesa <abel.vesa@linaro.org>