pfdi-sample-app: Introduce PFDI sample application

This commit introduces a sample pfdi application to demonstrate
the PFDI features.

The application supports both single and periodic modes of operation,
with periodic mode enabled by default. It takes platform fault detection
config data as input.

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