net: phy: realtek: fix enabling of the TX-delay for RTL8211F

The old logic always enabled the TX-delay when the phy-mode was set to
PHY_INTERFACE_MODE_RGMII. With this patch we enable the TX delay for
PHY_INTERFACE_MODE_RGMII_ID and PHY_INTERFACE_MODE_RGMII_TXID and
disable it for PHY_INTERFACE_MODE_RGMII.

Based on a similar change made in the Linux Realtek PHY driver
by Martin Blumenstingl <martin.blumenstingl@googlemail.com>.

Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: York Sun <york.sun@nxp.com>