mbedtls: enable support of hkdf

Adds the support of key derivation using
the scheme hkdf.

Reviewed-by: Raymond Mao <raymond.mao@linaro.org>
Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/lib/mbedtls/Kconfig b/lib/mbedtls/Kconfig
index 78167ff..aa82336 100644
--- a/lib/mbedtls/Kconfig
+++ b/lib/mbedtls/Kconfig
@@ -297,6 +297,13 @@
 	  This option enables support of hashing using MD5 algorithm
 	  with MbedTLS crypto library.
 
+config HKDF_MBEDTLS
+	bool "Enable HKDF support with MbedTLS crypto library"
+	depends on MBEDTLS_LIB_CRYPTO
+	help
+	  This option enables support of key derivation using HKDF algorithm
+	  with MbedTLS crypto library.
+
 if SPL
 
 config SPL_SHA1_MBEDTLS
@@ -335,6 +342,13 @@
 	  This option enables support of hashing using MD5 algorithm
 	  with MbedTLS crypto library.
 
+config SPL_HKDF_MBEDTLS
+	bool "Enable HKDF support in SPL with MbedTLS crypto library"
+	depends on MBEDTLS_LIB_CRYPTO
+	help
+	  This option enables support of key derivation using HKDF algorithm
+	  with MbedTLS crypto library.
+
 endif # SPL
 
 endif # MBEDTLS_LIB_CRYPTO