net: phy: add API to read 802.3-c45 IDs

Add API to read 802.3-c45 IDs so that C22/C45 mixed device can use
C45 APIs without failing ID checks.

Signed-off-by: Xu Liang <lxu@maxlinear.com>
Acked-by: Hauke Mehrtens <hmehrtens@maxlinear.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>