ARM: ep93xx: move network platform data to separate header

The header file is the only thing preventing us from building the
driver in a cross-platform configuration, so move the structure
we are interested in to the global platform_data location
and enable compile testing.

Acked-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>