zephyr: Use a smaller sha256 implementation
Reduce the size of the sha256 implementation by 1300 bytes by using a
slower implementation.
Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
diff --git a/boot/zephyr/include/config-rsa.h b/boot/zephyr/include/config-rsa.h
index 0552420..f07c457 100644
--- a/boot/zephyr/include/config-rsa.h
+++ b/boot/zephyr/include/config-rsa.h
@@ -64,6 +64,7 @@
#define MBEDTLS_MD_C
#define MBEDTLS_OID_C
#define MBEDTLS_SHA256_C
+#define MBEDTLS_SHA256_SMALLER
#define MBEDTLS_SHA224_C
#define MBEDTLS_AES_C