UPSTREAM: mm/damon/core: skip apply schemes if empty

Sometimes there is no scheme in damon's context, for example just use damo
record to monitor workload's data access pattern.

If current damon context doesn't have any scheme in the list, kdamond has
no need to iterate over list of all targets and regions but do nothing.

So, skip apply schemes when ctx->schemes is empty.

Link: https://lkml.kernel.org/r/20230116062347.1148553-1-huaisheng.ye@intel.com


Signed-off-by: Huaisheng Ye <huaisheng.ye@intel.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit 64517d6e)

Bug: 300502883
Bug: 317310896
Change-Id: Ic76ca90c85dbb24205b17dd914f91a8dd4cf7345
Signed-off-by: cui yangpei <cuiyangpei@xiaomi.com>