doc: enable building HTML doxygen

This will be posted to the cloud to ease review of changes to doxygen
modules and structure.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/doc/zephyr.doxyfile b/doc/zephyr.doxyfile
index 60420b3..06c018d 100644
--- a/doc/zephyr.doxyfile
+++ b/doc/zephyr.doxyfile
@@ -147,7 +147,7 @@
 #---------------------------------------------------------------------------
 # Configuration options related to the HTML output
 #---------------------------------------------------------------------------
-GENERATE_HTML          = NO
+GENERATE_HTML          = YES
 HTML_OUTPUT            = html
 HTML_FILE_EXTENSION    = .html
 HTML_HEADER            =