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>
diff --git a/arch/powerpc/xmon/ppc-opc.c b/arch/powerpc/xmon/ppc-opc.c
index af3780e..6845e91 100644
--- a/arch/powerpc/xmon/ppc-opc.c
+++ b/arch/powerpc/xmon/ppc-opc.c
@@ -22,6 +22,7 @@
 
 #include <linux/stddef.h>
 #include <linux/kernel.h>
+#include <linux/bug.h>
 #include "nonstdio.h"
 #include "ppc.h"