xgene_enet: remove bogus forward declarations

The device match tables for both the xgene_enet driver and its phy driver
have forward declarations that declare an array without a length, leading
to a clang warning when they are not followed by an actual defitinition:

drivers/net/ethernet/apm/xgene/../../../phy/mdio-xgene.h:135:34: warning: tentative array definition assumed to have one element
drivers/net/ethernet/apm/xgene/xgene_enet_main.c:33:36: warning: tentative array definition assumed to have one element

The declarations for the mdio driver are even in a header file, so they
cause duplicate definitions of the tables for each file that includes
them.

This removes all four forward declarations and moves the actual
definitions up a little, so they are in front of their first user. For
the OF match tables, this means having to remove the #ifdef around them,
and passing the actual structure into of_match_device(). This has no
effect on the generated object code though, as the of_match_device
function has an empty stub that does not evaluate its argument, and
the symbol gets dropped either way.

Fixes: 43b3cf66

 ("drivers: net: phy: xgene: Add MDIO driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>