hw/i386/pc: move shared x86 functions to x86.c and export them

Move x86 functions that will be shared between PC and non-PC machine
types to x86.c, along with their helpers.

Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 894989b..8920bd8 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -41,6 +41,7 @@
 #include "hw/pci-host/q35.h"
 #include "hw/qdev-properties.h"
 #include "exec/address-spaces.h"
+#include "hw/i386/x86.h"
 #include "hw/i386/pc.h"
 #include "hw/i386/ich9.h"
 #include "hw/i386/amd_iommu.h"