optvermaj.yml: Allow __RTEMS_MAJOR__ to be overridden so RTEMS 7 tools can be tested

spec/build/cpukit/optvermaj.yml

@@ -1,14 +1,16 @@
 SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
 actions:
-- set-value: '6'
+- get-string: null
 - env-assign: null
 build-type: option
 copyrights:
 - Copyright (C) 2020 embedded brains GmbH (http://www.embedded-brains.de)
-default: null
+default: 6
 default-by-variant: []
-description: ''
+description: |
+  Major Component of the RTEMS Version Number
 enabled-by: true
+format: '{}' 
 links: []
 name: __RTEMS_MAJOR__
 type: build