phy: mvebu-a3700-comphy: Inform users if their firmware is too old

PHY configuration has been implemented in the firmware and accessed
through SMC calls. In the past, it worked magically if the bootloader
was correctly doing the initializations.

With up-to-date bindings, the kernel will need a recent firmware in
order to do the initializations himself (we assume people must update
their firmware along with their kernel).

People might not understand why IPs that were working correctly before
stopped to be probed suddendly. In this case, let's advise the users
to update their firmware with a visual warning.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>