am335x: cpsw: optimize cpsw_send to increase network performance

Before submitting packets to cpdma, phy status is updated on every packet
which leads to delay in packet send intern reduces the Ethernet performance.
Checking mdio status for each packet will reduce timetaken to send a packet
and there by increasing the Ethernet performance. With this the performance
is increased from 208KiB/s to 375KiB/s on EVMsk

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>