mm/kfence: use special gfp_t format specifier

mm/kfence: use special gfp_t format specifier

%pGg produces nice readable output and decouples the format string from
the size of gfp_t.

Link: https://lore.kernel.org/20260326-gfp64-v2-3-d916021cecdf@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Allison Collins <allison.henderson@oracle.com>
Cc: Allison Henderson <achender@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marco Elver <elver@google.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislaw Gruszka <stf_xl@wp.pl>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>