This commit makes the monitoring operations for the physical address space
and virtual address spaces register themselves to DAMON in the
subsys_initcall step.  Later, in-kernel DAMON user code can use them via
damon_select_ops() without have to unnecessarily depend on all possible
monitoring operations implementations.

Link: https://lkml.kernel.org/r/20220215184603.1479-4-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Xin Hao <xhao@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>