Exempt PRE_BOOT_COMPLETED from timeout & deferral policy

PRE_BOOT_COMPLETED broadcast receivers are expected to possibly take a
long time to peform their work; they're doing significant work in
standing up the system itself.  Do not time out the broadcasts
themselves, and do not apply future broadcast deferral policy on the
basis of how long its receivers take to finish running.

Change-Id: I26469576d50400f3266cf6a5b09aa645fa83213a
Fixes: 117567005
Test: manual