ARM: ixp4xx: Delete the Freecom FSG-3 boardfiles

This board is replaced with the corresponding device tree.

Acked-by: Marc Zyngier <maz@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>