MIPS: update the MIPS u-boot.lds

From the document, if set all arguments in "OUTPUT_FORMAT" to
"tradbigmips", then even add "-EL" to gcc we still get EB format.

pb1x00 is only used in Little-endian, so its default endian should be
set to LE.

Signed-off-by: Xiangfu Liu <xiangfu@openmobilefree.net>
Signed-off-by: Shinya Kuribayashi <skuribay@pobox.com>