net: phylink: disable BMCR_ISOLATE in phylink_mii_c22_pcs_config

net: phylink: disable BMCR_ISOLATE in phylink_mii_c22_pcs_config

The Xilinx PCS/PMA PHY requires that BMCR_ISOLATE be disabled for proper
operation in 1000BaseX mode. It should be safe to ensure this bit is
disabled in phylink_mii_c22_pcs_config in all cases.

Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Reviewed-by: Russell King <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20201026175802.1332477-1-robert.hancock@calian.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>