mm/damon/core: disallow non-power of two min_region_sz on damon_start()

In the Linux kernel, the following vulnerability has been resolved: mm/damon/core: disallow non-power of two min_region_sz on damon_start() Commit d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region") introduced a bug that allows unaligned DAMON region address ranges. Commit c80f46ac228b ("mm/damon/core: disallow non-power of two min_region_sz") fixed it, but only for damon_commit_ctx() use case. Still, DAMON sysfs interface can emit non-power of two min_region_sz via damon_start(). Fix the path by adding the is_power_of_2() check on damon_start(). The issue was discovered by sashiko [1].