mm: kmemleak: add CONFIG_DEBUG_KMEMLEAK_VERBOSE build option

mm: kmemleak: add CONFIG_DEBUG_KMEMLEAK_VERBOSE build option

Add a Kconfig option to default kmemleak verbose mode on at build time.
This option depends on DEBUG_KMEMLEAK_AUTO_SCAN since verbose reporting is
only meaningful when the automatic scanning thread is running.

When enabled, kmemleak prints full details (backtrace, hex dump, address)
of unreferenced objects to dmesg as they are detected during scanning,
removing the need to manually read /sys/kernel/debug/kmemleak.

Making this a compile-time option rather than a boot parameter allows
debug kernel flavors to enable verbose kmemleak reporting by default
without requiring changes to boot arguments.  A machine can simply swap to
a debug kernel and benefit from kmemleak reporting automatically.

By surfacing leak reports directly in dmesg, they are automatically
forwarded through any kernel logging infrastructure and can be easily
captured by log aggregation tooling, making it practical to monitor memory
leaks across large fleets.

The verbose setting can still be toggled at runtime via
/sys/module/kmemleak/parameters/verbose.

Link: https://lore.kernel.org/20260323-kmemleak_report-v1-1-ba2cdd9c11b9@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: SeongJae Park <sj@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>