plat: imx8mq: enable cpuidle support on iMX8MQ

Refact the PSCI  related code. Enable cpuidle support
on i.MX8MQ for CPU idle support.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
(cherry picked from commit 34fbf7a35c83c879a0ca385b0200858641ca37b4)
6 files changed