Remove tf-psa-crypto/include/mbedtls/private from Doxygen

Signed-off-by: Felix Conway <felix.conway@arm.com>
diff --git a/doxygen/mbedtls.doxyfile b/doxygen/mbedtls.doxyfile
index 04a4f17..00e64d0 100644
--- a/doxygen/mbedtls.doxyfile
+++ b/doxygen/mbedtls.doxyfile
@@ -8,6 +8,7 @@
 CASE_SENSE_NAMES       = NO
 INPUT                  = ../include input ../tf-psa-crypto/include ../tests/include/alt-dummy
 FILE_PATTERNS          = *.h
+EXCLUDE                = ../tf-psa-crypto/include/mbedtls/private
 RECURSIVE              = YES
 EXCLUDE_SYMLINKS       = YES
 SOURCE_BROWSER         = YES