MIPS: BMIPS: select CPU_SUPPORTS_HIGHMEM

All BMIPS CPUs support HIGHMEM, so it should be selected by CPU_BMIPS.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6242/