Merge branch 'master' of https://source.denx.de/u-boot/custodians/u-boot-sunxi

This cleans up each board's defconfig, and fixes the serial console on
some Olimex board. Also we lose another legacy config variable.
The rest are minor cleanups, that actually shouldn't change anything
in the build.

Passed the gitlab CI, plus briefly tested on Pine64-LTS, LicheePi Nano,
and BananaPi M1.