dm: verity-loadpin: Use CONFIG_SECURITY_LOADPIN_VERITY for conditional compilation

The verity glue for LoadPin is only needed when CONFIG_SECURITY_LOADPIN_VERITY
is set, use this option for conditional compilation instead of the combo of
CONFIG_DM_VERITY and CONFIG_SECURITY_LOADPIN.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Acked-by: Mike Snitzer <snitzer@kernel.org>
Link: https://lore.kernel.org/lkml/20220627083512.v7.3.I5aca2dcc3b06de4bf53696cd21329dce8272b8aa@changeid


Signed-off-by: Kees Cook <keescook@chromium.org>