allwinner: implement system power down on H6 w/ AXP805
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The AXP805 PMIC used with H6 is capable of shutting down the system.
Add support for using it to shut down the system power.
The original placeholder power off code is moved to A64 code, as it's
still TODO to implement PMIC operations for A64.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
As the ATF may need to do some power initialization on Allwinner
platform with AXP PMICs, call the PMIC setup code in BL31.
Stub of PMIC setup code is added, to prevent undefined reference.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
