doxygen: enable the search engine

Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/doxygen/mbedtls.doxyfile b/doxygen/mbedtls.doxyfile
index 8cc87d6..b4f255e 100644
--- a/doxygen/mbedtls.doxyfile
+++ b/doxygen/mbedtls.doxyfile
@@ -17,7 +17,7 @@
 ALPHABETICAL_INDEX     = NO
 HTML_OUTPUT            = .
 HTML_TIMESTAMP         = YES
-SEARCHENGINE           = NO
+SEARCHENGINE           = YES
 GENERATE_LATEX         = NO
 INCLUDE_PATH           = ../include
 CLASS_DIAGRAMS         = NO