arm-bsp-extras/conf/rd-aspen: Add PFDI_SUPPORT option

Add a variable PFDI_SUPPORT which can be used to control
whether to add Platform Fault Detection Interface support
to RD-Aspen or not. This variable can be later used to
enable or disable PFDI in the CI.

Signed-off-by: Ziad Elhanafy <ziad.elhanafy@arm.com>