test: add rsa_verify() unit test

In this patch, a very simple test is added to verify that rsa_verify()
using rsa_verify_with_pkey() work correctly.

To keep the code simple, all the test data, either public key and
verified binary data, are embedded in the source.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
diff --git a/test/lib/Makefile b/test/lib/Makefile
index 230068d..ce9ae4a 100644
--- a/test/lib/Makefile
+++ b/test/lib/Makefile
@@ -8,4 +8,5 @@
 obj-y += string.o
 obj-$(CONFIG_ERRNO_STR) += test_errno_str.o
 obj-$(CONFIG_UT_LIB_ASN1) += asn1.o
+obj-$(CONFIG_UT_LIB_RSA) += rsa.o
 obj-$(CONFIG_AES) += test_aes.o