crypto: use validateObject

The `validateObject()` validator can be used to cleanup validation and
keep consistency.

lib/internal/crypto/keys.js

@@ -299,8 +299,7 @@ function isStringOrBuffer(val) {
 }
 
 function parseKeyEncoding(enc, keyType, isPublic, objName) {
-  if (enc === null || typeof enc !== 'object')
-    throw new ERR_INVALID_ARG_TYPE('options', 'object', enc);
+  validateObject(enc, 'options');
 
   const isInput = keyType === undefined;