net: bcmgenet: Fix attaching to PYH failed on RPi 4B

net: bcmgenet: Fix attaching to PYH failed on RPi 4B

The Broadcom UniMAC MDIO bus from mdio-bcm-unimac module comes too late.
So, GENET cannot find the ethernet PHY on UniMAC MDIO bus. This leads
GENET fail to attach the PHY as following log:

bcmgenet fd580000.ethernet: GENET 5.0 EPHY: 0x0000
...
could not attach to PHY
bcmgenet fd580000.ethernet eth0: failed to connect to PHY
uart-pl011 fe201000.serial: no DMA platform data
libphy: bcmgenet MII bus: probed
...
unimac-mdio unimac-mdio.-19: Broadcom UniMAC MDIO bus

This patch adds the soft dependency to load mdio-bcm-unimac module
before genet module to avoid the issue.

Fixes: e6ac242ee955 ("net: bcmgenet: utilize generic Broadcom UniMAC MDIO controller driver")
Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=213485
Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>