doc/fvp-rd-aspen: Update RAS validation

- Updated the method of validating RAS error processing.
- Updated components to include the TF-A-tests and its
downstream changes.
- Updated validation section of the docs to mention RAS
validation.
- Updated release notes about RAS error handling.

Signed-off-by: Michael Zhao <michael.zhao2@arm.com>
Signed-off-by: Ahmed Azeem <ahmed.azeem@arm.com>