net: stmmac: only call pmt() during suspend/resume if HW enables PMT

This is to prepare WOL support with phy. Compared with WOL
implementation which relies on the MAC's PMT features, in phy
supported WOL case, device_may_wakeup() may also be true, but we
should not call mac's pmt() function if HW doesn't enable PMT.

And during resume, we should call phylink_start() if PMT is disabled.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>