net: asix: Fix ASIX 88772B with driver model

Commit 14727120 ("net: asix: fix operation without eeprom")
added a special handling for ASIX 88772B that enable another
type of header. This break the driver in DM mode as the extra handling
needed in the receive path is missing.

However this new header mode is not required and only seems to
increase the code complexity, so this patch revert this part of
commit 14727120.

This also reverts commit 41d1258a
("net: asix: Fix AX88772B when used with DriverModel") of late.

Fixes: 14727120 ("net: asix: fix operation without eeprom")

Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>