stmmac: add GMAC4 DMA/CORE Header File

This is the main header file to define all the
macro used for GMAC4 DMA and CORE parts.

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