ARM: dts: am5729: beaglebone-ai: fix rgmii phy-mode

Since commit cd28d1d6 ("net: phy: at803x: Disable phy delay for
RGMII mode") the networking is broken on the BeagleBone AI which has
the AR8035 PHY for Gigabit Ethernet [0].  The fix is to switch from
phy-mode = "rgmii" to phy-mode = "rgmii-rxid".

Note: Grygorii made a similar DT fix for other AM57xx boards with a
different phy in commit 820f8a87 ("ARM: dts: am57xx: fix networking
on boards with ksz9031 phy").

[0] https://git.io/Jf7PX



Fixes: 520557d4 ("ARM: dts: am5729: beaglebone-ai: adding device tree")
Cc: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
Signed-off-by: Drew Fustini <drew@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>