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/kernel_compat.c

@@ -0,0 +1,30 @@
+#include "linux/version.h"
+#include "linux/init.h"
+#include "linux/fs.h"
+ssize_t kernel_read_compat(struct file *p, void *buf, size_t count, loff_t *pos){
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
+    return kernel_read(p, buf, count, pos);
+#else
+    loff_t offset = pos ? *pos : 0;
+    ssize_t result = kernel_read(p, offset, (char *)buf, count);
+    if (pos && result > 0)
+    {
+        *pos = offset + result;
+    }
+    return result;
+#endif
+}
+
+ssize_t kernel_write_compat(struct file *p, const void *buf, size_t count, loff_t *pos){
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
+    return kernel_write(p, buf, count, pos);
+#else
+    loff_t offset = pos ? *pos : 0;
+    ssize_t result = kernel_write(p, buf, count, offset);
+    if (pos && result > 0)
+    {
+        *pos = offset + result;
+    }
+    return result;
+#endif
+}