net: stmmac: socfpga: convert to stmmac_pltfr_pm_ops

Convert socfpga to use the generic stmmac_pltfr_pm_ops, which can be
achieved by adding an appropriate plat_dat->init function to do the
setup.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/E1u5Sni-001IJk-Gi@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>