logd: Add support for ro.logd.auditd.[main|events]

log selinux audit messages boolean (true or false, default true)
selection for logging destinations:

ro.logd.auditd - turn on logd.auditd to pick up violations.
ro.logd.auditd.dmesg - to the kernel log.
ro.logd.auditd.main - to the "main" log buffer.
ro.logd.auditd.events - to the "events" log buffer.

We used to also read logd.auditd.dmesg and persist.logd.auditd.dmesg
which do not get refreshed when /data mounts internally.  This is a
confusing state as these properties will be read after a logd crash
and restart, adjusting the behavior of the logger.  Same can be said
for logd.auditd as well.  Drop reading these other parameters.

Test: manual set r/o parameters, stop/start logd to confirm behavior
Bug: 33969000
Bug: 27878170
Change-Id: I1a6bb4a903074c9aa7b227cf583a0094d49cbefd