net: phy: add qca8081 read_status

1. Separate the function at803x_read_specific_status from
the at803x_read_status, since it can be reused by the
read_status of qca8081 phy driver excepting adding the
2500M speed.

2. Add the qca8081 read_status function qca808x_read_status.

Signed-off-by: Luo Jie <luoj@codeaurora.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>