This version field exposes the (already present) version information of a boot
parameters file.
* gnu/system.scm (%boot-parameters-version): New variable.
(<boot-parameters>)[version]: New field.
(read-boot-parameters): Use it.
(operating-system-boot-parameters-file): Likewise.
* tests/boot-parameters.scm (test-read-boot-parameters): Use
%boot-parameters-version as the default version value in the template.