MIPS: BCM63xx: Utilize asm/bmips-spaces.h

Since BCM63xx runs on BMIPS3300 which requires the use of a FIXADDR_TOP
to avoid collisions with the SBR, utilize asm/bmips-spaces.h which
defines FIXADDR_TOP for us now.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: blogic@openwrt.org
Cc: cernekee@chromium.org
Cc: jogo@openwrt.org
Patchwork: https://patchwork.linux-mips.org/patch/9969/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>