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/net/pcnet.c b/hw/net/pcnet.c
index b0b462b..b606d2b 100644
--- a/hw/net/pcnet.c
+++ b/hw/net/pcnet.c
@@ -41,7 +41,7 @@
 #include "qemu/sockets.h"
 #include "sysemu/sysemu.h"
 
-#include "hw/pcnet.h"
+#include "pcnet.h"
 
 //#define PCNET_DEBUG
 //#define PCNET_DEBUG_IO