feat(morello): add cpuidle support

This patch adds necessary device-tree idle state definitions and enables
relevant platform makefile options.

Co-authored-by: Karl Meakin <karl.meakin@arm.com>
Signed-off-by: sahil <sahil@arm.com>
Change-Id: Iaf95867095f0514ec3994b9c9efd9756ed49ef43
3 files changed