stmmac: add init/exit callback in plat_stmmacenet_data struct

This patch adds in the plat_stmmacenet_data
the init and exit callbacks that can be used
for invoking specific platform functions.
For example, on ST targets, these call the
PAD manager functions to set PIO lines and
syscfg registers.
The patch removes the stmmac_claim_resource
only used on STM Kernels as well.

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