By Evan Garcia and Jonathan Allen MEMPHIS, Tenn. (Reuters) -Hundreds of mourners gathered at Graceland on Sunday morning to pay their respects to singer Lisa Marie Presley in a memorial service at the mansion in Memphis, Tennessee, she inherited from her father, rock legend Elvis Presley. Presley died on Jan. 12 at the age of 54. Earlier that day, she had been rushed to a Los Angeles-area hospital after reportedly suffering cardiac arrest at her home. “Our heart is broken, Lisa, and we all love you,” her mother, Priscilla Presley, said at the service on the front lawn of Graceland. “Lisa Marie…