Some older socs like the rk3288 do not have the necessary registers
to check the wfi/wfe state of the cpu cores. Allow this case an "just"
do an additional delay similar to how the Linux kernel handles smp
right now.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Change-Id: I0f67af388b06b8bfb4a9bac411b4900ac266a77a