stmmac: fix ptp init for gmac4

The gmac 4.x version has not extended descriptors
(that are available on 3.x instead of).
While initializing the PTP module, the advanced PTP was
enabled in case of extended descriptors. This cannot be
applied for 4.x version where only the hardware capability
register has to show if the feature is present.
Patch also adds some extra netdev_(debug/inof) to better
dump the configuration.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre TORGUE <alexandre.torgue@st.com>
Cc: Rayagond Kokatanur <rayagond@vayavyalabs.com>
Signed-off-by: David S. Miller <davem@davemloft.net>