hw: move private headers to hw/ subdirectories.

Many headers are used only in a single directory.  These can be
kept in hw/.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/arm/strongarm.c b/hw/arm/strongarm.c
index 0e5262d..5873a3c 100644
--- a/hw/arm/strongarm.c
+++ b/hw/arm/strongarm.c
@@ -27,7 +27,7 @@
  *  GNU GPL, version 2 or (at your option) any later version.
  */
 #include "hw/sysbus.h"
-#include "hw/strongarm.h"
+#include "strongarm.h"
 #include "qemu/error-report.h"
 #include "hw/arm.h"
 #include "char/char.h"