ANDROID: gki_defconfig: enable CONFIG_KFENCE_STATIC_KEYS

The default value of this option changed recently in
4f612ed3 ("kfence: default to dynamic branch instead of static keys
mode"). As there was no functional change here and no concern posed
about configurations relevant to Android, re-enable this option.

Bug: 234805737
Signed-off-by: Steve Muckle <smuckle@google.com>
Change-Id: I5b20a67225cd247fc54547083b3cbcde0135f1fb