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/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index d90272e..83e7b81 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -26,6 +26,7 @@
 
 #include <asm/bug.h>
 #include <asm/paravirt.h>
+#include <asm/debugreg.h>
 #include <asm/desc.h>
 #include <asm/setup.h>
 #include <asm/pgtable.h>