ARM: dts: imx6dl-yapp4: Fix RGMII connection to QCA8334 switch

ARM: dts: imx6dl-yapp4: Fix RGMII connection to QCA8334 switch

BugLink: https://bugs.launchpad.net/bugs/1933691
commit 0e4a4a08cd78efcaddbc2e4c5ed86b5a5cb8a15e upstream.

The FEC does not have a PHY so it should not have a phy-handle. It is
connected to the switch at RGMII level so we need a fixed-link sub-node
on both ends.

This was not a problem until the qca8k.c driver was converted to PHYLINK
by commit b3591c2a3661 ("net: dsa: qca8k: Switch to PHYLINK instead of
PHYLIB"). That commit revealed the FEC configuration was not correct.

Fixes: 87489ec3a77f ("ARM: dts: imx: Add Y Soft IOTA Draco, Hydra and Ursa boards")
Cc: stable@vger.kernel.org
Signed-off-by: Michal Vokáč <michal.vokac@ysoft.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>