uboot-mediatek: add missing LED command for OpenWrt One

uboot-mediatek: add missing LED command for OpenWrt One

The u-boot LED command "led_loop_done" is missing from the OpenWrt
One NAND flash u-boot. Copy it from the OpenWrt One NOR flash u-boot
default environment to fix this issue.

Fixes: https://github.com/openwrt/openwrt/issues/17310
Signed-off-by: Shiji Yang <yangshiji66@qq.com>
Link: https://github.com/openwrt/openwrt/pull/17338
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 5ef71eaafd4e128ec3708a66b5633214427da373)