Add missing declaration of SHA-224 from MBEDTLS_SHA256_C

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/config_psa.h b/include/mbedtls/config_psa.h
index f16be60..69a6a31 100644
--- a/include/mbedtls/config_psa.h
+++ b/include/mbedtls/config_psa.h
@@ -315,6 +315,7 @@
 #if defined(MBEDTLS_SHA256_C)
 #define MBEDTLS_PSA_BUILTIN_ALG_SHA_224 1
 #define MBEDTLS_PSA_BUILTIN_ALG_SHA_256 1
+#define PSA_WANT_ALG_SHA_224 1
 #define PSA_WANT_ALG_SHA_256 1
 #endif