kernel: backport to 4.4 (#166)

These changes make KernelSU work on kernel4.4
[link](https://github.com/F-19-F/android_kernel_oneplus_msm8998).
LINUX_VERSION_CODE macro changes have been vertied on 4.4 4.9 4.14.
For kernel 4.4,just pick two commits
* [introduce
KernelSU](2993524f2f)
* [allow init exec ksud under
nosuid](3df9df42a6)

kernel/Makefile

@@ -9,6 +9,7 @@ obj-y += manager.o
 obj-y += core_hook.o
 obj-y += ksud.o
 obj-y += embed_ksud.o
+obj-y += kernel_compat.o
 
 obj-y += selinux/