Add encoded points to other EC curves too.

Add encoded point ctrl support for other curves: this makes it possible
to handle X25519 and other EC curve point encoding in a similar way
for TLS.

Reviewed-by: Rich Salz <rsalz@openssl.org>

crypto/ec/ec_ameth.c

diff --git a/crypto/ec/ec_ameth.c b/crypto/ec/ec_ameth.c
index b1dc011..f6a3f5c 100644
--- a/crypto/ec/ec_ameth.c
+++ b/crypto/ec/ec_ameth.c
@@ -496,6 +496,13 @@
         *(int *)arg2 = NID_sha256;
         return 2;
 
+    case ASN1_PKEY_CTRL_SET1_TLS_ENCPT:
+        return EC_KEY_oct2key(EVP_PKEY_get0_EC_KEY(pkey), arg2, arg1, NULL);
+
+    case ASN1_PKEY_CTRL_GET1_TLS_ENCPT:
+        return EC_KEY_key2buf(EVP_PKEY_get0_EC_KEY(pkey),
+                              POINT_CONVERSION_UNCOMPRESSED, arg2, NULL);
+
     default:
         return -2;