ar71xx: set mips16 support, tune cflags for 34kc (works well on MIPS 24K as well, but helps a lot for 34K and 74K)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36600 3c298f89-4303-0410-b956-a3cf2f4a3e73
px5g: disable assembler functions, fixes compile errors with mips16

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36601 3c298f89-4303-0410-b956-a3cf2f4a3e73