platform: Modifying arm vsi header file license

- Modifying arm_vsi.h header file's Arm license as the current
license cause the CI to fail as it is not of the same format
that we use for our license header
(ex SPDX-License-Identifier: Apache-2.0)

- Applying clang's format to the file.

Signed-off-by: Ahmed.Ismail <Ahmed.Ismail@arm.com>