net: phy: smsc: LAN8710/20: add phy refclk in support

Add support to specify the clock provider for the PHY refclk and don't
rely on 'magic' host clock setup. [1] tried to address this by
introducing a flag and fixing the corresponding host. But this commit
breaks the IRQ support since the irq setup during .config_intr() is
thrown away because the reset comes from the side without respecting the
current PHY state within the PHY library state machine. Furthermore the
commit fixed the problem only for FEC based hosts other hosts acting
like the FEC are not covered.

This commit goes the other way around to address the bug fixed by [1].
Instead of resetting the device from the side every time the refclk gets
(re-)enabled it requests and enables the clock till the device gets
removed. Now the PHY library is the only place where the PHY gets reset
to respect the PHY library state machine.

[1] commit 7f64e5b1

 ("net: phy: smsc: LAN8710/20: add
    PHY_RST_AFTER_CLK_EN flag")

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>