cassini-[doc,config,distro,tests]: Add PARSEC support

Added parsec-service and parsec-tool support to Cassini stack.

Introduced a new DISTRO_FEATURE `cassini-parsec` to conditionally
enable/disable PARSEC support. Added simple e2e tests from parsec-tool
as integration test for parsec-service.

Changelog: feature
Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>