stmmac: intel: set PCI_D3hot in suspend

During suspend, set the Intel mgbe to D3hot state
to save power consumption.

Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>
Signed-off-by: Ling Pei Lee <pei.lee.ling@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>