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.
diff --git a/scripts/.gitignore b/scripts/.gitignore
index e2741d2..105b21f 100644
--- a/scripts/.gitignore
+++ b/scripts/.gitignore
@@ -8,3 +8,4 @@
 unifdef
 ihex2fw
 recordmcount
+docproc