net: phy: introduce phy_read_poll_timeout macro

it is sometimes necessary to poll a phy register by phy_read()
function until its value satisfies some condition. introduce
phy_read_poll_timeout() macros that do this.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>