Makefile: enable dochelp run from main make level

Change to enable dochelp run from main make level to make it easier to
use it.

Signed-off-by: Shuah Khan <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
diff --git a/Makefile b/Makefile
index d111994..bcb20d2 100644
--- a/Makefile
+++ b/Makefile
@@ -1454,7 +1454,7 @@
 
 # Documentation targets
 # ---------------------------------------------------------------------------
-DOC_TARGETS := xmldocs latexdocs pdfdocs htmldocs epubdocs cleandocs linkcheckdocs
+DOC_TARGETS := xmldocs latexdocs pdfdocs htmldocs epubdocs cleandocs linkcheckdocs dochelp
 PHONY += $(DOC_TARGETS)
 $(DOC_TARGETS): scripts_basic FORCE
 	$(Q)$(MAKE) $(build)=Documentation $@