net: stmmac: socfpga: provide init function

Both the resume and probe path needs to configure the phy mode, so
provide a common function to do this which can later be hooked into
plat_dat->init.

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/E1u5Snd-001IJe-Cx@rmk-PC.armlinux.org.uk


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