minimal build fixes for uml (fallout from x86 merge)

 a) include/asm-um/arch can't just point to include/asm-$(SUBARCH) now
 b) arch/{i386,x86_64}/crypto are merged now
 c) subarch-obj needed changes
 d) cpufeature_64.h should pull "cpufeature_32.h", not <asm/cpufeature_32.h>
    since it can be included from asm-um/cpufeature.h
 e) in case of uml-i386 we need CONFIG_X86_32 for make and gcc, but not
    for Kconfig
 f) sysctl.c shouldn't do vdso_enabled for uml-i386 (actually, that one
    should be registered from corresponding arch/*/kernel/*, with ifdef
    going away; that's a separate patch, though).

With that and with Stephen's patch ("[PATCH net-2.6] uml: hard_header fix")
we have uml allmodconfig building both on i386 and amd64.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/Makefile-x86_64 b/arch/um/Makefile-x86_64
index 69ecea6..8a00e5f 100644
--- a/arch/um/Makefile-x86_64
+++ b/arch/um/Makefile-x86_64
@@ -1,7 +1,7 @@
 # Copyright 2003 - 2004 Pathscale, Inc
 # Released under the GPL
 
-core-y += arch/um/sys-x86_64/ arch/x86_64/crypto/
+core-y += arch/um/sys-x86_64/ arch/x86/crypto/
 START := 0x60000000
 
 _extra_flags_ = -fno-builtin -m64
@@ -18,6 +18,7 @@
 
 ELF_ARCH := i386:x86-64
 ELF_FORMAT := elf64-x86-64
+HEADER_ARCH := x86
 
 # Not on all 64-bit distros /lib is a symlink to /lib64. PLD is an example.