kernel: ath10k: provide a build variant for small RAM devices

kernel: ath10k: provide a build variant for small RAM devices

Based on: 1ac627024de9 ("kernel: ath10k-ct: provide a build variant for
small RAM devices")

Like described in the ath10k-ct-smallbuffers version, oom-killer gets
triggered frequently by devices with small RAM.

That change is necessary for many community mesh networks which use
ath10k based devices with too little RAM. The -ct driver has been
proven unstable if used with 11s meshing and only wave2 chipsets are
supporting 11s. Freifunk Berlin is nowadays assembling its
firmware-based completely of vanilla OpenWRT with some package additions
which are made through the imagebuilder. Therefore we cannot take the
approach other freifunk communities have taken to maintain that patch
downstream [1]. Other communities consider these devices as broken and
that change would pretty much give those devices a second life [2].
[1] - https://git.freifunk-franken.de/mirror/openwrt/commit/450b306e540bc0f2c8a8841bbe4d9612f2b8cdea
[2] - https://github.com/freifunk-gluon/gluon/issues/1988#issuecomment-619532909

Signed-off-by: Simon Polack <spolack+git@mailbox.org>
Signed-off-by: Nick Hainke <vincent@systemli.org>
(cherry picked from commit 694757a08f620a9f24b70003542d9dcd0abeac46)