kernel: Reformat code using clang-format (#347)

* The coding format is too messy, reformat to improve readability
  and get closer to Linux kernel coding style.

* While at it, update .clang-format file to linux-mainline state.

kernel/kpm/compact.h

@@ -1,6 +1,6 @@
 #ifndef ___SUKISU_KPM_COMPACT_H
 #define ___SUKISU_KPM_COMPACT_H
 
-unsigned long sukisu_compact_find_symbol(const char* name);
+unsigned long sukisu_compact_find_symbol(const char *name);
 
 #endif