sunxi: psci: implement PSCI on R528

This patch adds the necessary code to make nonsec booting and PSCI
secondary core management functional on the R528/T113.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>
Tested-by: Maksim Kiselev <bigunclemax@gmail.com>
Tested-by: Kevin Amadiva <kevin.amadiva@mec.at>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>