xen/arm: introduce CONFIG_XEN on ARM

Changes in v5:

- make XEN_DOM0 depend on XEN;
- avoid "select XEN_DOM0" in XEN.


Changes in v2:

- mark Xen guest support on ARM as EXPERIMENTAL.

Signed-off-by: Stefano Stabellini <[e-mail]>
CC: Sergei Shtylyov <[e-mail]>

arch/arm/Kconfig

···
 	  This was deprecated in 2001 and announced to live on for 5 years.
 	  Some old boot loaders still use this way.
 
+config XEN_DOM0
+	def_bool y
+	depends on XEN
+
+config XEN
+	bool "Xen guest support on ARM (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && ARM && OF
+	help
+	  Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
+
 endmenu
 
 menu "Boot options"