MIPS: Octeon: Remove special handling of CONFIG_MIPS_ELF_APPENDED_DTB=y

The ELF appended dtb can be accessed now via 'fw_passed_dtb'.

Since raw appended dtb is accessed via that variable too,
this now effectively allows to boot with CONFIG_MIPS_RAW_APPENDED_DTB=y
on Octeon.

Signed-off-by: Yasha Cherikovsky <yasha.che3@gmail.com>
[paul.burton@mips.com: Fix trivial __dtb_octeon_*_begin conflict]
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20805/
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