net: phy: enhance GPY115 loopback disable function

GPY115 need reset PHY when it comes out from loopback mode if the firmware
version number (lower 8 bits) is equal to or below 0x76.

Fixes: 7d901a1e ("net: phy: add Maxlinear GPY115/21x/24x driver")
Signed-off-by: Xu Liang <lxu@maxlinear.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>