VIENNA, July 14 (Reuters) - U.S. Secretary of State John Kerry on Monday expressed his deep concern to Bahrain Foreign minister Khaled al-Khalifa over the expulsion of a U.S. diplomat for meeting with an opposition leader and over charges brought against the politician. A senior State Department official said Kerry, who was in Vienna for talks between Iran and major powers over curbing Tehran's nuclear program, spoke by telephone with the Bahraini minister. ...