ARM: imx25: Remove eukrea mx25 board files

eukrea mx25 is well supported in device tree, so let's get rid of its board
files.

Cc: Eric Bénard <eric@eukrea.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>