Compile some MIPS devices only once

Move CPU specific declarations to a separate file.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/mips_malta.c b/hw/mips_malta.c
index 96e3bc0..9a35d0c 100644
--- a/hw/mips_malta.c
+++ b/hw/mips_malta.c
@@ -31,6 +31,7 @@
 #include "block.h"
 #include "flash.h"
 #include "mips.h"
+#include "mips_cpudevs.h"
 #include "pci.h"
 #include "usb-uhci.h"
 #include "vmware_vga.h"