net: netsec: Ignore 'phy-mode' on SynQuacer in DT mode

As documented in acd7aaf5 ("netsec: ignore 'phy-mode' device
property on ACPI systems") the SocioNext SynQuacer platform ships with
firmware defining the PHY mode as RGMII even though the physical
configuration of the PHY is for TX and RX delays.  Since bbc4d71d
("net: phy: realtek: fix rtl8211e rx/tx delay config") this has caused
misconfiguration of the PHY, rendering the network unusable.

This was worked around for ACPI by ignoring the phy-mode property but
the system is also used with DT.  For DT instead if we're running on a
SynQuacer force a working PHY mode, as well as the standard EDK2
firmware with DT there are also some of these systems that use u-boot
and might not initialise the PHY if not netbooting.  Newer firmware
imagaes for at least EDK2 are available from Linaro so print a warning
when doing this.

Fixes: 533dd11a

 ("net: socionext: Add Synquacer NetSec driver")
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230731-synquacer-net-v3-1-944be5f06428@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>