In the beginning was a really obnoxious trumpet, and the trumpet was with M.I.A. , and the trumpet sort of was M.I.A., insofar as a split-second sample of the Rocky theme tune could represent a musician’s entire way of being in the world. A loud noise torn from its source, demanding attention. BLAARP. The plasticky fanfare of that ’70s horn (plundered from Bill Conti for the art school rapper’s breakout single “ Bucky Done Gun ”) makes a prophetic return, seven times over, on M.I.7 —an emotional and ecstatic testament to personal salvation, which is, as advertised, M.I.A.’s gospel album. Fearless, naive, maddening, vindicated, and forever courting controversy, M.I.A. has been working at the intersection of art and the artist for over 20 years. She’s always rapped with the old-time swagger and conviction of Chuck D, mixing playground boasts with the hard facts of an unequal system: guns, borders, refugees, cops.…