net: dsa: microchip: Make switch detection more informative

To make switch detection more informative print the result of the
ksz9477/ksz9893 compatibility check. With debug output enabled also
print the contents of the Chip ID registers as a 40-bit hex string.

As this detection is the first communication with the switch performed
by the driver, making it easy to see any errors here will help identify
issues with SPI data corruption or reset sequencing.

Signed-off-by: Paul Barker <pbarker@konsulko.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>