MIPS: Export string functions alongside their definitions

Now that EXPORT_SYMBOL can be used from assembly source, move the
EXPORT_SYMBOL invocations for the strlen*, strnlen* & strncpy* functions
to be alongside their definitions.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14513/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>