Implement the CSS driver for A83T

[smaeul]

Linux has existing code for this in https://github.com/torvalds/linux/blob/master/arch/arm/mach-sunxi/mc_smp.c. Need to evaluate how much of this can be shared with the existing CSS drivers.

[ghost]

Linux at this moment doesn't even use PSCI on A83T. I have added some code to Linux, that suspends all cores except the boot one (via in-kernel code you linked), and then sends a message to crust via SCPI to shut down the last core. So in my world crust only needs to shut down the last core/cluster and whatever else it wants.

Looking at crust CSS drivers and adding A83T variant of the code is my next planned step.