kbuild: move autoconf.h to include/generated

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Documentation/kbuild/kconfig.txt

@@ -106,7 +106,8 @@ This environment variable can be set to specify the path & name of the
 KCONFIG_AUTOHEADER
 --------------------------------------------------
 This environment variable can be set to specify the path & name of the
-"autoconf.h" (header) file.  Its default value is "include/linux/autoconf.h".
+"autoconf.h" (header) file.
+Its default value is "include/generated/autoconf.h".
 
 
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