lmkd: Do not set soft_limit_in_bytes on high-end devices

Setting memory.soft_limit_in_bytes on high-end devices with large memory
reserves affects performance of memory-hungry applications that have
large workingsets and keep thrashing because of the memory limits imposed.
Limit the usage of memory.soft_limit_in_bytes to low-memory devices only.
Add debug messages for future troubleshooting to capture cases when
vmpressure events are being ignored.

Bug: 78916015
Test: collect vmstat while running a heavy app
Change-Id: Ib4434b96d2be802ef89960b573486eae8d12f198
Merged-In: Ib4434b96d2be802ef89960b573486eae8d12f198
Signed-off-by: Suren Baghdasaryan <surenb@google.com>