riscv: dts: starfive: remove "snps,en-tx-lpi-clockgating" property

riscv: dts: starfive: remove "snps,en-tx-lpi-clockgating" property

Whether the MII transmit clock can be stopped is primarily a property
of the PHY (there is a capability bit that should be checked first.)
Whether the MAC is capable of stopping the transmit clock is a separate
issue, but this is already handled by the core DesignWare MAC code.

As commit "net: stmmac: starfive: use PHY capability for TX clock stop"
adds the flag to use the PHY capability, remove the DT property that is
now unecessary.

Cc: Samin Guo <samin.guo@starfivetech.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tsIU5-005vGR-4c@rmk-PC.armlinux.org.uk
Signed-off-by: Paolo Abeni <pabeni@redhat.com>