rasdaemon: Fix mem_fail_event build breakage

rasdaemon: Fix mem_fail_event build breakage

Commit 566a52622b1d ("add mem_fail_event trigger") introduces an event
trigger for a memory failure event.

However, if the rasdaemon is not configured with enable-memory-failure,
the setup function of the trigger, mem_fail_event_trigger_setup(), will
result in an undefined reference linker error when called through
setup_event_trigger().

Ensure that the setup function for the trigger is called only when the
rasdaemon has been configured with enable-memory-failure.

Fixes: 566a52622b1d ("add mem_fail_event trigger")
Signed-off-by: Avadhut Naik <avadhut.naik@amd.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>