lxt PHY: Support for the buggy LXT973 rev A2

This patch adds proper handling of the buggy revision A2 of LXT973 phy, adding
precautions linked to ERRATA Item 4:

Revision A2 of LXT973 chip randomly returns the contents of the previous even
register when you read a odd register regularly

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>