bug.h: add include of it to various implicit C users

With bug.h currently living right in linux/kernel.h there
are files that use BUG_ON and friends but are not including
the header explicitly.  Fix them up so we can remove the
presence in kernel.h file.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

arch/x86/mm/kmemcheck/selftest.c

@@ -1,3 +1,4 @@
+#include <linux/bug.h>
 #include <linux/kernel.h>
 
 #include "opcode.h"