openssl/lk: Enable signed boot img check

This uses openssl to check the boot image prior
to jumping to kernel to see if it is a signed
kernel image.

Change-Id: I92927fd9317a0f701dab395cc6d39929c64340c1
diff --git a/platform/init.c b/platform/init.c
index 11bcb8b..49e6e75 100644
--- a/platform/init.c
+++ b/platform/init.c
@@ -60,3 +60,11 @@
 __WEAK void platform_uninit(void)
 {
 }
+
+__WEAK int image_verify(unsigned char * image_ptr,
+			unsigned char * signature_ptr,
+			unsigned int image_size,
+			unsigned hash_type)
+{
+	return 0;
+}