generic: 6.6: backport arm64 swiotlb default size reduction

generic: 6.6: backport arm64 swiotlb default size reduction

Kernel 6.6 added dynamic SWIOTLB allocation, but with it also started
allocating 64MB of the SWIOTLB bounce buffer by default which is quite a
lot of memory on most OpenWrt devices.

Luckily in kernel 6.7 arm64 received an optimization that reduces that
default size to 1MB per 1GB of RAM if certain criteria was met.

So in order to reclaim back 63MB of RAM which brought some ipq807x devices
close to OOM under load lets backport the upstream commit.

Signed-off-by: Robert Marko <robimarko@gmail.com>