The outgoing license was MIT only. The new dual license allows
using the code under Apache-2.0 WITH LLVM-exception license too.

Use standard name for the LICENSE file.

Use consistent license text across files:
- "ARM" is changed to Arm,
- "All Rights Reserved" is dropped (not needed),
- "This file is part of.." is dropped,
- Text is formatted as is recommended by the LICENSE file.