toolchain-headers: also copy asm-eva.h for mips(el) for 3.15+

Kernel 3.15's asm.h includes eva-asm.h, so copy it also, else lzma-loader
won't compile due to a missing include.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43460 3c298f89-4303-0410-b956-a3cf2f4a3e73
brcm63xx: add kernel 3.18 support

Add 3.18 support based on 3.18-rc6. Only netboot tested.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43461 3c298f89-4303-0410-b956-a3cf2f4a3e73