uml: Kconfig cleanup

pointed out by Linus: arch/um/Kconfig.x86_64 should
include arch/x86/Kconfig.cpu instead of defining those
symbols itself.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/um/Kconfig.x86_64

+
+menu "Host processor type and features"
+
+source "arch/x86/Kconfig.cpu"
+
+endmenu
+
 config UML_X86
 	bool
 	default y