linux-postmarketos-allwinner: various improvements from other MRs (anbox, ipv4 wireguard, nftables, leds-gpio max_brightness)

Rebase patches from the currently open allwinner-related MRs with minor changes into one MR, so they can be tested together.

• !1798: enable Anbox networking options
• !1831: Add IPv4 support for wireguard-tools
• !1832: set leds-gpio max_brightness to 1
• !1833 (closed): enable nftables support
• !1750: Add 'pine64,pinephone' to DTS compatible list

Close: #909 (closed), #480 (closed), !1798, !1831, !1832, !1833 (closed)

The individual MRs have already been reviewed by others, and they also look good to me. I'll do the full kernel upgrade test with this one, and try to test anbox networking too, and merge it afterwards.

CC: @alpabrz, @craftyguy, @dylanvanassche, @edp17, @afontain