Replace MBEDTLS_MD_CAN_SHA256 in md.h, ssl.h, and entropy.h

Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/tf-psa-crypto/drivers/builtin/include/mbedtls/entropy.h b/tf-psa-crypto/drivers/builtin/include/mbedtls/entropy.h
index 20fd687..57af02a 100644
--- a/tf-psa-crypto/drivers/builtin/include/mbedtls/entropy.h
+++ b/tf-psa-crypto/drivers/builtin/include/mbedtls/entropy.h
@@ -22,7 +22,7 @@
 #define MBEDTLS_ENTROPY_MD  MBEDTLS_MD_SHA512
 #define MBEDTLS_ENTROPY_BLOCK_SIZE      64      /**< Block size of entropy accumulator (SHA-512) */
 #else
-#if defined(MBEDTLS_MD_CAN_SHA256)
+#if defined(PSA_WANT_ALG_SHA_256)
 #define MBEDTLS_ENTROPY_SHA256_ACCUMULATOR
 #define MBEDTLS_ENTROPY_MD  MBEDTLS_MD_SHA256
 #define MBEDTLS_ENTROPY_BLOCK_SIZE      32      /**< Block size of entropy accumulator (SHA-256) */