runtime: get k*alloc and kfree functions into scope

Get k*alloc and kfree functions into scope since they are defined both
in runtime/runtime.h and runtime/linux/runtime.h.

Signed-off-by: Apelete Seketeli <apelete@seketeli.net>
stapify: automatically find kernel output directory

Kernel output directory can change depending on the Android source
tree in use, so try to find it by searching for System.map file.

Signed-off-by: Apelete Seketeli <apelete@seketeli.net>
stapify: add cross-compile flag depending on machine type detection

When host machine is x86_64 and target is i?86, add '-a i386'
cross-compile flag in order to build .stp script into kernel module.

Signed-off-by: Apelete Seketeli <apelete@seketeli.net>