By Chris Rosvoglou With Marcus Mariota no longer on the roster, the Las Vegas Raiders are officially in the market for a backup quarterback. Though a deal isn’t imminent at this time, the Raiders may have found an ideal target to assume the No. 2 role on the depth chart. According to NFL Network’s James Palmer, former New Orleans Saints quarterback Trevor Siemian is visiting with the Raiders this Thursday. Siemian, 30, appeared in six games for the Saints this past season. He completed 57.4 percent of his passes for 1,154 yards and 11 touchdowns. The Raiders aren’t the only team showing intere…