uboot-layerscape: adjust LS1012A-IOT config and env

In a254279a6c30 LS1012A-IOT kernel image was switched to FIT.

But u-boot config is lack of FIT and ext4 support.

This patch enables it.

It also fix envs, because for some reason this board need to use "loadaddr"
variable in brackets.

Fixes: #9894
Fixes: a254279a6c30 ("layerscape: Change to combined rootfs on sd images")
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>