Move x86 specific PC declarations to a separate file

x86 definitions (especially CPUState uses) prevent many files from
being compiled within libhw.

Move x86 specific declarations (APIC stuff) to a separate file.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/apic.c b/hw/apic.c
index 3c90f4c..9029dad 100644
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -18,6 +18,7 @@
  */
 #include "hw.h"
 #include "pc.h"
+#include "apic.h"
 #include "pci.h"
 #include "msix.h"
 #include "qemu-timer.h"