MIPS: strip the un-needed sections of vmlinuz

This patch use "strip -s" to strip the .symtab and .strtab sections of
vmlinuz.

Note: This patch is based on http://patchwork.linux-mips.org/patch/1324/



Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1383/


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