MIPS: Ensure ELF appended dtb is relocated

This fixes booting with the combination of CONFIG_RELOCATABLE=y
and CONFIG_MIPS_ELF_APPENDED_DTB=y.

Sections that appear after the relocation table are not relocated
on system boot (except .bss, which has special handling).

With CONFIG_MIPS_ELF_APPENDED_DTB, the dtb is part of the
vmlinux ELF, so it must be relocated together with everything else.

Fixes: 069fd766

 ("MIPS: Reserve space for relocation table")
Signed-off-by: Yasha Cherikovsky <yasha.che3@gmail.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v4.7+