MIPS: BMIPS: Define BMIPS_FIXADDR_TOP in asm/bmips-spaces.h

The FIXADDR_TOP value used by mach-bmips is in fact required whenever we
run on BMIPS3300 BMIPS CPUs, and is not machine, but CPU-specific, move
this constant to asm/bmips-spaces.h and use it in mach-bmips/spaces.h.

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/9968/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>