Change Code: ${EXT_CARD}p1 -> ${EXT_CARD}p5 and Code: init=/bin /systemd -> init=/bin/systemd and it should boot. You don't need to copy uImage anywhere if you configure uboot to look under /boot for it, like you've already done. Good luck.
${EXT_CARD}p1 -> ${EXT_CARD}p5
init=/bin /systemd -> init=/bin/systemd
mmc0 is current device ** Bad partition 5 **
run emmcboot
Kernel Panic - not syncing: VFS: Unable to mount rootfs on unknown-block(179,5)