stmmac: dwmac-sti: move st, gmac_en parsing to sti_dwmac_parse_data

The sti_dwmac_init() function is called both from probe and resume.
Since DT properties doesn't change between suspend/resume cycles move
parsing of this parameter into sti_dwmac_parse_data() where it belongs.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Tested-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>