arm64: dts: rockchip: Enable HDD power on helios64

arm64: dts: rockchip: Enable HDD power on helios64

This adds the hdd_{a,b}_power blocks present in the armbian helios64
dts. [1]

Without those powered up, no HDDs will appear (except one connected via
the m.2 slot).

>From https://wiki.kobol.io/helios64/sata/#hdd-power:

> The power delivery of the HDDs is divided into two group:
>
>     HDD Rail A (Max. 3x Drives)
>     HDD Rail B (Max. 2x Drives)
>
> Helios64 implements a power staggering approach where HDD Rail A will be
> powered up first, then few seconds later HDD Rail B will be powered up.
> This power control scenario is performed to reduce the inrush current
> during disk spin-up.

In practice, this power staggering approach will be included in the
bootloader (not in the kernel), as we might want to boot from a SATA
drive.

>From my experiments, if the bootloader doesn't implement the power
staggering, only one HDD will get recognized (probably cause the others
didn't boot due to few power).

Still, it makes sense to expose this block in the device-tree, so the
kernel can ensure both rails are on (and this can be shared with
u-boot).

[1] https://github.com/armbian/build/blob/744ea89a589d62cb6f409baab60fc6664520bc39/patch/kernel/archive/rockchip64-5.14/add-board-helios64.patch

Signed-off-by: Florian Klink <flokli@flokli.de>
Tested-by: Dennis Gilmore <dgilmore@redhat.com>
Link: https://lore.kernel.org/r/20211020095926.735938-1-flokli@flokli.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>