uniphier: work around Boot ROM bug for USB boot mode of PXs3 SoC

Due to a bug in the Boot ROM, the USB load API turned out not working
as expected.  It is unfixable because the Boot ROM is hard-wired.

Add work around code in TF to bypass the problematic Boot ROM code.

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