MIPS: Move vmlinux.ecoff to arch/mips/boot

It moves to the same directory as the boot files in other formats.

Signed-off-by: Yoichi Yuasa <yuasa@linux-mips.org>
Cc: linux-mips <linux-mips@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/796/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>