net: cadence: macb: Expose REFCLK as a device tree property

net: cadence: macb: Expose REFCLK as a device tree property

The RMII and RGMII can both support internal or external provided
REFCLKs 50MHz and 125MHz respectively. Since this is dependent on
the board that the SoC is on this needs to be set via the device tree.

This property flag is checked in the MACB DT node so the REFCLK cap is
configured the correct way for the RMII or RGMII is configured on the
board.

Signed-off-by: Ryan Wanner <Ryan.Wanner@microchip.com>
Link: https://patch.msgid.link/7f9b65896d6b7b48275bc527b72a16347f8ce10a.1752510727.git.Ryan.Wanner@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>