net: broadcom: Select BROADCOM_PHY for BCMGENET

The GENET controller on the Raspberry Pi 4 (2711) is typically
interfaced with an external Broadcom PHY via a RGMII electrical
interface. To make sure that delays are properly configured at the PHY
side, ensure that we the dedicated Broadcom PHY driver
(CONFIG_BROADCOM_PHY) is enabled for this to happen.

Fixes: 402482a6

 ("net: bcmgenet: Clear ID_MODE_DIS in EXT_RGMII_OOB_CTRL when not needed")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>