rules.mk: MIPS16 builds get a different toolchain

To be safe, build "m16" into the toolchain and target architecture the
same way mips32r2 does:

target-mips_r2_m16_uClibc-0.9.33.2
toolchain-mips_r2_m16_gcc-4.6-linaro_uClibc-0.9.33.2

Signed-off-by: Jay Carlson <nop@nop.com>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36198 3c298f89-4303-0410-b956-a3cf2f4a3e73