hw: move headers to include/

Many of these should be cleaned up with proper qdev-/QOM-ification.
Right now there are many catch-all headers in include/hw/ARCH depending
on cpu.h, and this makes it necessary to compile these files per-target.
However, fixing this does not belong in these patches.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/piix4.c b/hw/piix4.c
index 0f5cd01..d750413 100644
--- a/hw/piix4.c
+++ b/hw/piix4.c
@@ -23,9 +23,9 @@
  */
 
 #include "hw/hw.h"
-#include "hw/pc.h"
+#include "hw/i386/pc.h"
 #include "hw/pci/pci.h"
-#include "hw/isa.h"
+#include "hw/isa/isa.h"
 #include "hw/sysbus.h"
 
 PCIDevice *piix4_dev;