Introduce CONFIG_XEN_PVHVM compile option

This patch introduce a CONFIG_XEN_PVHVM compile time option to
enable/disable Xen PV on HVM support.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index b83e119..68128a1 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -13,6 +13,11 @@
 	  kernel to boot in a paravirtualized environment under the
 	  Xen hypervisor.
 
+config XEN_PVHVM
+	def_bool y
+	depends on XEN
+	depends on X86_LOCAL_APIC
+
 config XEN_MAX_DOMAIN_MEMORY
        int "Maximum allowed size of a domain in gigabytes"
        default 8 if X86_32