x86: introduce CONFIG_GUEST and move code

Xen is able to run as a guest on Xen. We plan to make it able to run
on Hyper-V as well.

Introduce CONFIG_GUEST which is set to true if either running on Xen
or Hyper-V is desired. Restructure code hierarchy for new code to
come.

No functional change intended.

Signed-off-by: Wei Liu <liuwe@microsoft.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/Kconfig

@@ -161,9 +161,12 @@ config XEN_ALIGN_2M
 
 endchoice
 
+config GUEST
+	bool
+
 config XEN_GUEST
-	def_bool n
-	prompt "Xen Guest"
+	bool "Xen Guest"
+	select GUEST
 	---help---
 	  Support for Xen detecting when it is running under Xen.
 

xen/arch/x86/Makefile

@@ -1,7 +1,7 @@
 subdir-y += acpi
 subdir-y += cpu
 subdir-y += genapic
-subdir-$(CONFIG_XEN_GUEST) += guest
+subdir-$(CONFIG_GUEST) += guest
 subdir-$(CONFIG_HVM) += hvm
 subdir-y += mm
 subdir-$(CONFIG_XENOPROF) += oprofile

xen/arch/x86/guest/Makefile

@@ -1,4 +1 @@
-obj-y += hypercall_page.o
-obj-y += xen.o
-
-obj-bin-$(CONFIG_PVH_GUEST) += pvh-boot.init.o
+subdir-$(CONFIG_XEN_GUEST) += xen

xen/arch/x86/guest/xen/Makefile

@@ -0,0 +1,4 @@
+obj-y += hypercall_page.o
+obj-y += xen.o
+
+obj-bin-$(CONFIG_PVH_GUEST) += pvh-boot.init.o