Revert "net: mvneta: fix usage as a module on RGMII configurations"

This reverts commit e3a8786c. While
this commit allows to use the mvneta driver as a module on some
configurations, it breaks other configurations even if mvneta is used
built-in.

This breakage is due to the fact that on some RGMII platforms, the PCS
bit has to be set, and on some other platforms, it has to be
cleared. At the moment, we lack informations to know exactly the
significance of this bit (the datasheet only says "enables PCS"), and
so we can't produce a patch that will work on all platforms at this
point. And since this change is breaking the network completely for
many users, it's much better to revert it for now. We'll come back
later with a proper fix that takes into account all platforms.

Basically:

 * Armada XP GP is configured as RGMII-ID, and needs the PCS bit to be
   set.
 * Armada 370 Mirabox is configured as RGMII-ID, and needs the PCS bit
   to be cleared.

And at the moment, we don't know how to make the distinction between
those two cases. One hint is that the Armada XP GP appears in fact to
be using a QSGMII connection with the PHY (Quad-SGMII), but
configuring it as SGMII doesn't work, while RGMII-ID works. This needs
more investigation, but in the mean time, let's unbreak the network
for all those users.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reported-by: Arnaud Ebalard <arno@natisbad.org>
Reported-by: Alexander Reuter <Alexander.Reuter@gmx.net>
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=73401


Cc: stable@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>