Merge tag 'dm-pull-21oct21' of https://source.denx.de/u-boot/custodians/u-boot-dm

Refactoring of env_get_char() etc.
Update buildman to use gcc-11.1.0
Use in-container toolchain for nokia_rx51 CI test

# gpg: Signature made Thu 21 Oct 2021 09:34:07 PM EDT
# gpg:                using RSA key B25C0022AF86A7CC1655B6277F173A3E9008ADE6
# gpg:                issuer "sjg@chromium.org"
# gpg: Good signature from "Simon Glass <sjg@chromium.org>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: B25C 0022 AF86 A7CC 1655  B627 7F17 3A3E 9008 ADE6