xen: factor out common functions

So common functions used by both HVM and PV are factored out from
xen-all.c to xen-common.c.

Finally rename xen-all.c to xen-hvm.c, as those functions are only
useful to HVM guest.

Create *-stub files and modify Makefile.target to reflect the changes.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

xen-hvm-stub.c

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2010       Citrix Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ * Contributions after 2012-01-13 are licensed under the terms of the
+ * GNU GPL, version 2 or (at your option) any later version.
+ */
+
+#include "qemu-common.h"
+#include "hw/xen/xen.h"
+#include "exec/memory.h"
+#include "qmp-commands.h"
+
+int xen_pci_slot_get_pirq(PCIDevice *pci_dev, int irq_num)
+{
+    return -1;
+}
+
+void xen_piix3_set_irq(void *opaque, int irq_num, int level)
+{
+}
+
+void xen_piix_pci_write_config_client(uint32_t address, uint32_t val, int len)
+{
+}
+
+void xen_hvm_inject_msi(uint64_t addr, uint32_t data)
+{
+}
+
+void xen_cmos_set_s3_resume(void *opaque, int irq, int level)
+{
+}
+
+void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, MemoryRegion *mr)
+{
+}
+
+qemu_irq *xen_interrupt_controller_init(void)
+{
+    return NULL;
+}
+
+void xen_register_framebuffer(MemoryRegion *mr)
+{
+}
+
+void xen_modified_memory(ram_addr_t start, ram_addr_t length)
+{
+}
+
+int xen_hvm_init(MemoryRegion **ram_memory)
+{
+    return 0;
+}
+
+void qmp_xen_set_global_dirty_log(bool enable, Error **errp)
+{
+}