Fix parsing of PKCS#8 encoded Elliptic Curve keys.

The relevant ASN.1 definitions for a PKCS#8 encoded Elliptic Curve key are:

PrivateKeyInfo ::= SEQUENCE {
  version                   Version,
  privateKeyAlgorithm       PrivateKeyAlgorithmIdentifier,
  privateKey                PrivateKey,
  attributes           [0]  IMPLICIT Attributes OPTIONAL
}

AlgorithmIdentifier  ::=  SEQUENCE  {
  algorithm   OBJECT IDENTIFIER,
  parameters  ANY DEFINED BY algorithm OPTIONAL
}

ECParameters ::= CHOICE {
  namedCurve         OBJECT IDENTIFIER
  -- implicitCurve   NULL
  -- specifiedCurve  SpecifiedECDomain
}

ECPrivateKey ::= SEQUENCE {
  version        INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
  privateKey     OCTET STRING,
  parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
  publicKey  [1] BIT STRING OPTIONAL
}

Because of the two optional fields, there are 4 possible variants that need to
be parsed: no optional fields, only parameters, only public key, and both
optional fields. Previously mbedTLS was unable to parse keys with "only
parameters". Also, only "only public key" was tested. There was a test for "no
optional fields", but it was labelled incorrectly as SEC.1 and not run because
of a great renaming mixup.
diff --git a/tests/suites/test_suite_pkparse.data b/tests/suites/test_suite_pkparse.data
index 91d2408..cbbbd5b7 100644
--- a/tests/suites/test_suite_pkparse.data
+++ b/tests/suites/test_suite_pkparse.data
@@ -992,10 +992,6 @@
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 pk_parse_keyfile_ec:"data_files/ec_prv.sec1.der":"NULL":0
 
-Parse EC Key #1a (SEC1 DER, no optional part)
-depends_on:POLARSSL_PEM_PARSE_C:POLARSSL_ECP_C:POLARSSL_ECP_DP_SECP256R1_ENABLED
-pk_parse_keyfile_ec:"data_files/ec_prv.noopt.der":"NULL":0
-
 Parse EC Key #2 (SEC1 PEM)
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 pk_parse_keyfile_ec:"data_files/ec_prv.sec1.pem":"NULL":0
@@ -1008,10 +1004,34 @@
 depends_on:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 pk_parse_keyfile_ec:"data_files/ec_prv.pk8.der":"NULL":0
 
+Parse EC Key #4a (PKCS8 DER, no public key)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+pk_parse_keyfile_ec:"data_files/ec_prv.pk8nopub.der":"NULL":0
+
+Parse EC Key #4b (PKCS8 DER, no public key, with parameters)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+pk_parse_keyfile_ec:"data_files/ec_prv.pk8nopubparam.der":"NULL":0
+
+Parse EC Key #4c (PKCS8 DER, with parameters)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+pk_parse_keyfile_ec:"data_files/ec_prv.pk8param.der":"NULL":0
+
 Parse EC Key #5 (PKCS8 PEM)
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 pk_parse_keyfile_ec:"data_files/ec_prv.pk8.pem":"NULL":0
 
+Parse EC Key #5a (PKCS8 PEM, no public key)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+pk_parse_keyfile_ec:"data_files/ec_prv.pk8nopub.pem":"NULL":0
+
+Parse EC Key #5b (PKCS8 PEM, no public key, with parameters)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+pk_parse_keyfile_ec:"data_files/ec_prv.pk8nopubparam.pem":"NULL":0
+
+Parse EC Key #5c (PKCS8 PEM, with parameters)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+pk_parse_keyfile_ec:"data_files/ec_prv.pk8param.pem":"NULL":0
+
 Parse EC Key #6 (PKCS8 encrypted DER)
 depends_on:MBEDTLS_DES_C:MBEDTLS_SHA1_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 pk_parse_keyfile_ec:"data_files/ec_prv.pk8.pw.der":"polar":0