plat: imx8m: Keep A53 PLAT on in wait mode(ret)

Keep A53 PLAT(SCU) power domain on in wait mode(ret).
RBC count only need to be set in PLAT OFF mode, so
change it accordingly.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: Ie55e25c8210d298506fc4dca7a9653583db45e0c
2 files changed