net: phy: marvell10g: add thermal hwmon device

Add a thermal monitoring device for the Marvell 88x3310, which updates
once a second.  We also need to hook into the suspend/resume mechanism
to ensure that the thermal monitoring is reconfigured when we resume.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>