mlxbf_gige: Fix intermittent no ip issue

Although the link is up, there is no ip assigned on setups with high background
traffic. Nothing is transmitted nor received. The RX error count keeps on
increasing. After several minutes, the RX error count stagnates and the
GigE interface finally gets an ip.

The issue is that mlxbf_gige_rx_init() is called before phy_start().
As soon as the RX DMA is enabled in mlxbf_gige_rx_init(), the RX CI reaches the max
of 128, and becomes equal to RX PI. RX CI doesn't decrease since the code hasn't
ran phy_start yet.
Bring the PHY up before starting the RX.

Fixes: f92e1869

 ("Add Mellanox BlueField Gigabit Ethernet driver")
Reviewed-by: David Thompson <davthompson@nvidia.com>
Signed-off-by: Asmaa Mnebhi <asmaa@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>