ARM: add Kconfig option for PSCI 0.1

ARM: add Kconfig option for PSCI 0.1

We still have some platforms that only implements functionalities in
PSCI 0.1 (e.g. Allwinner ARMv7 SoCs).

Add a Kconfig option for exporting only PSCI 0.1. The code to export
PSCI 0.1 is still available and gets activated by this patch.

In addition, default ARCH_SUNXI U-Boot PSCI implementation to export
PSCI 0.1, to fix poweroff/reboot regression on Allwinner multi-core
ARMv7 SoCs.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>