This commit does the following:
- Adds SPDX license identifiers to FreeRTOS sources. Remove those FreeRTOS sources from
the copyright ignore list.
- Update xtensa port files to match FreeRTOS v10.4.3. Added SPDX license identifiers
to the port files.
- Fixed some improperly licensed files
- Removed portbenchmark.h from RISC-V port