x86, um: untangle uml ldt.h

* turn asm/ldt.h into ldt.h; update the (very few) users
* take host_ldt.h into sysdep, kill symlink mess
* includes of asm/arch/ldt.h turn into asm/ldt.h now

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/um/include/shared/um_mmu.h

@@ -8,7 +8,7 @@
 
 #include "uml-config.h"
 #include "mm_id.h"
-#include "asm/ldt.h"
+#include "ldt.h"
 
 typedef struct mm_context {
 	struct mm_id id;