uboot-imx

iot_dk: Link for eFlash

That's what we'll have in production.
But note it won't work for loading via JTAG as
eFlash is not directly writable, one needs to use
prebootloader to flash uboot.bin from SD-card into eFlash.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>