uboot-phytec

arm/km: drop unneeded define

CONFIG_BOOTCOUNT_LIMIT is used on all boards from this board series. So
remove this unneeded define.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Acked-by: Valentin Longchamp <valentin.longchamp@keymile.com>