After internal testing and review, we reached the conclusion that using -p to
both define and filter platforms was too confusing and difficult to teach.
Additionally, there are concerns that use of flags to define platforms may not
scale, since real-life use-cases may require more than a list of commands.

This commit is a partial revert of intel#49: the ability to filter platforms
remains, but the ability to define platforms directly via JSON is removed.

Signed-off-by: John Pennycook <john.pennycook@intel.com>

Signed-off-by: John Pennycook <john.pennycook@intel.com>

Signed-off-by: John Pennycook <john.pennycook@intel.com>

Separates legacy behavior (YAML files) and modern behavior (TOML files).
When using TOML files, the output name is updated to reflect the subset
of platforms that were actually included in the analysis.

Signed-off-by: John Pennycook <john.pennycook@intel.com>

Signed-off-by: John Pennycook <john.pennycook@intel.com>