net: dsa: mv88e6xxx: Avoid EEPROM timeout without EEPROM on 88E6250-family switches

88E6250-family switches have the quirk that the EEPROM Running flag can
get stuck at 1 when no EEPROM is connected, causing
mv88e6xxx_g2_eeprom_wait() to time out. We still want to wait for the
EEPROM however, to avoid interrupting a transfer and leaving the EEPROM
in an invalid state.

The condition to wait for recommended by the hardware spec is the EEInt
flag, however this flag is cleared on read, so before the hardware reset,
is may have been cleared already even though the EEPROM has been read
successfully.

For this reason, we revive the mv88e6xxx_g1_wait_eeprom_done() function
that was removed in commit 6ccf50d4
("net: dsa: mv88e6xxx: Avoid EEPROM timeout when EEPROM is absent") in a
slightly refactored form, and introduce a new
mv88e6xxx_g1_wait_eeprom_done_prereset() that additionally handles this
case by triggering another EEPROM reload that can be waited on.

On other switch models without this quirk, mv88e6xxx_g2_eeprom_wait() is
kept, as it avoids the additional reload.

Fixes: 6ccf50d4 ("net: dsa: mv88e6xxx: Avoid EEPROM timeout when EEPROM is absent")
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>