use simplified VHDL file headers

[stnolting]

Update all core rtl files with the new simplified file headers:

-- ================================================================================ --
-- FULL MODULE NAME; ONE LINE                                                       --
-- -------------------------------------------------------------------------------- --
-- OPTIONAL BRIEF DESCRIPTION                                                       --
-- -------------------------------------------------------------------------------- --
-- The NEORV32 RISC-V Processor - https://github.com/stnolting/neorv32              --
-- Copyright (c) NEORV32 contributors.                                              --
-- Copyright (c) 2020 - 2024 Stephan Nolting. All rights reserved.                  --
-- Licensed under the BSD-3-Clause license, see LICENSE for details.                --
-- SPDX-License-Identifier: BSD-3-Clause                                            --
-- ================================================================================ --

On a very rainy Sunday I might also update all the remaining file headers... 🙈😅