stmmac: add new DT platform entries for GMAC4

This is to support the snps,dwmac-4.00 and snps,dwmac-4.10a
and related features on the platform driver.
See binding doc for further details.

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