kbuild: move asm-offsets.h to include/generated

The simplest method was to add an extra asm-offsets.h
file in arch/$ARCH/include/asm that references the generated file.

We can now migrate the architectures one-by-one to reference
the generated file direct - and when done we can delete the
temporary arch/$ARCH/include/asm/asm-offsets.h file.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michal Marek <mmarek@suse.cz>

arch/um/Makefile

@@ -149,6 +149,6 @@ $(SHARED_HEADERS)/user_constants.h: $(ARCH_DIR)/sys-$(SUBARCH)/user-offsets.s
 
 $(SHARED_HEADERS)/kern_constants.h:
 	$(Q)mkdir -p $(dir $@)
-	$(Q)echo '#include "../../../../include/asm/asm-offsets.h"' >$@
+	$(Q)echo '#include "../../../../include/generated/asm-offsets.h"' >$@
 
 export SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING OS HEADER_ARCH DEV_NULL_PATH

arch/um/include/asm/asm-offsets.h

+#include <generated/asm-offsets.h>

arch/x86/include/asm/asm-offsets.h

+#include <generated/asm-offsets.h>

arch/xtensa/include/asm/asm-offsets.h

+#include <generated/asm-offsets.h>