ARM: ixp4xx: Delete Gateway 7001 boardfiles

This board is replaced with the corresponding device tree.

Cc: Imre Kaloz <kaloz@openwrt.org>
Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220211223238.648934-2-linus.walleij@linaro.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>