net: stmmac: Fix MAC WoL not working if PHY does not support WoL

Both get and set WoL will check device_can_wakeup(), if MAC supports PMT, it
will set device wakeup capability. After commit 1d8e5b0f ("net: stmmac:
Support WOL with phy"), device wakeup capability will be overwrite in
stmmac_init_phy() according to phy's Wol feature. If phy doesn't support WoL,
then MAC will lose wakeup capability. To fix this issue, only overwrite device
wakeup capability when MAC doesn't support PMT.

For STMMAC now driver checks MAC's WoL capability if MAC supports PMT, if
not support, driver will check PHY's WoL capability.

Fixes: 1d8e5b0f ("net: stmmac: Support WOL with phy")
Reviewed-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>