[MIPS] vmlinux.lds.S: handle .text.*

The -ffunction-sections puts each text in .text.function_name section.
Without this patch, most functions are placed outside _text..._etext
area and it breaks show_stacktrace(), etc.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>