Now everything is done to load a raw U-Boot proper image instead of
an mkimage-processed one (as far as I tested on NAND, eMMC, NOR).

The SPL already knows the load address of the U-Boot proper without
parsing its uImage header because the load address is defined by
CONFIG_SYS_TEXT_BASE, assuming that the two images are generated from
the same build.

My main motivation of this switch is to use u-boot-with-spl.bin, a
concatenation of u-boot-spl.bin and u-boot.bin.  (I wish there were
a concatenation of u-boot-spl.bin and u-boot.img...)  Anyway, this
commit would be useful for one-shot image burn.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>