net: phy: add qca8081 config_init

Add the qca8081 phy driver config_init function, which includes:
1. Enable fast restrain.
2. Add 802.3az configurations.
3. Initialize ADC threshold as 100mv.

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