Stop using inline string functions on MIPS as other ARCHs do so,
since the optimized inline asm versions are not small.
This change is triggered by a following MIPS build error:
common/libcommon.a(exports.o)(.text+0xdc): In function `jumptable_init':
common/exports.c:32: undefined reference to `strcmp'
make: *** [u-boot] Error 1
Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi@necel.com>