arm64: dts: allwinner: Add Allwinner H616 .dtsi file

This (relatively) new SoC is similar to the H6, but drops the (broken)
PCIe support and the USB 3.0 controller. It also gets the management
controller removed, which in turn removes *some*, but not all of the
devices formerly dedicated to the ARISC (CPUS).
And while there is still the extra sunxi interrupt controller, the
package lacks the corresponding NMI pin, so no interrupts for the PMIC.

The reserved memory node is actually handled by Trusted Firmware now,
but U-Boot fails to propagate this to a separately loaded DTB, so we
keep it in here for now, until U-Boot learns to do this properly.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>