kbuild: move scripts/basic/docproc.c to scripts/docproc.c

Move docproc from scripts/basic to scripts so it is only built for *doc
targets instead of every time the kernel is built.

scripts/Makefile

diff --git a/scripts/Makefile b/scripts/Makefile
index fcea261..df7678f 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -6,6 +6,7 @@
 # pnmttologo:    Convert pnm files to logo files
 # conmakehash:   Create chartable
 # conmakehash:	 Create arrays for initializing the kernel console tables
+# docproc:       Used in Documentation/DocBook
 
 hostprogs-$(CONFIG_KALLSYMS)     += kallsyms
 hostprogs-$(CONFIG_LOGO)         += pnmtologo
@@ -16,12 +17,14 @@
 always		:= $(hostprogs-y) $(hostprogs-m)
 
 # The following hostprogs-y programs are only build on demand
-hostprogs-y += unifdef
+hostprogs-y += unifdef docproc
 
-# This target is used internally to avoid "is up to date" messages
+# These targets are used internally to avoid "is up to date" messages
 PHONY += build_unifdef
 build_unifdef: scripts/unifdef FORCE
 	@:
+build_docproc: scripts/docproc FORCE
+	@:
 
 subdir-$(CONFIG_MODVERSIONS) += genksyms
 subdir-y                     += mod