Make SCP broadcast protected

As we are removing the Privileged receiver in CellBroadcastReceiver, we
should ensure that the SCP broadcast (in addition to the SMS_CB
broadcast, which is already protected) can only be sent by system.

Bug: 148482594
Test: manually verify that the broadcast can only be sent from system
Change-Id: I94feaecda633507604321ed23f39026a7e77b3df
Merged-In: I94feaecda633507604321ed23f39026a7e77b3df
1 file changed