x86, um: get rid of arch/um/Kconfig.arch

Teach scripts/kconfig/Makefile and top-level Makefile that arch/*/Makefile
is allowed to say Kconfig := <whatever I want instead of arch/blah/Kconfig>.
Rewrite arch/um/Kconfig and arch/um/Kconfig.<subarch> so that the latter
would be top-level one (and include the pieces of the former).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/um/Kconfig.x86 b/arch/um/Kconfig.x86
index 76200c9..5ee3280 100644
--- a/arch/um/Kconfig.x86
+++ b/arch/um/Kconfig.x86
@@ -1,3 +1,7 @@
+source "arch/um/Kconfig.common"
+
+menu "UML-specific options"
+
 menu "Host processor type and features"
 
 source "arch/x86/Kconfig.cpu"
@@ -44,3 +48,9 @@
 
 config GENERIC_HWEIGHT
 	def_bool y
+
+source "arch/um/Kconfig.um"
+
+endmenu
+
+source "arch/um/Kconfig.rest"