barebox: use lz4 instead of lz4c

barebox: use lz4 instead of lz4c

lz4c has been considered deprecated by upstream since at least 2018 [1]
and has been disabled by default recently [2].  openSUSE Tumbleweed is
no longer packaging the deprecated version and others will likely
follow.

Going back as far as Ubuntu 16.04/Fedora 25, both lz4 and lz4c are
installed as part of the same package so switching should be safe.

1. https://github.com/lz4/lz4/pull/553
2. https://github.com/lz4/lz4/pull/1479

Upstream-Status: Submitted [http://lists.infradead.org/pipermail/barebox/2024-November/048491.html]
Signed-off-by: Justin Bronder <jsbronder@cold-front.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>