[ARM] 5273/2: ep93xx: move ethernet support into core.c

All EP93xx based systems can support Ethernet. This patch moves
the platform_device setup from the various board support files
into the core support file. The Ethernet driver data still remains
in the individual platform setup files to allow specific platform
configuration.

This also adds Ethernet support to the edb9302, edb9312, and
edb9315 platforms.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>