net: ftgmac100: select FIXED_PHY

Depending on e.g. DT configuration this driver uses a fixed link.
So we shouldn't rely on the user to enable FIXED_PHY, select it in
Kconfig instead. We may end up with a non-functional driver otherwise.

Fixes: 38561ded ("net: ftgmac100: support fixed link")
Cc: stable@vger.kernel.org
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/476bb33b-5584-40f0-826a-7294980f2895@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>