pfdi-tool: Introduce pfdi-tool

This commit introduces pfdi-tool, which provides the following
operations:

- generate pfdi test config file
- validate pfdi test config file
- fix pfdi test config file
- pack pfdi test config file

These operations are used to prepare and pfdi test config to run
the pfdi-app.

Signed-off-by: Ziad Elhanafy <ziad.elhanafy@arm.com>
Signed-off-by: Divin Raj <divin.raj@arm.com>