When SPN is empty, use PNN in mobile network settings

Added one more name source 'PNN', which has priority
higher than carrier id but lower than EF_SPN.

Bug: 143493866
Test: Manual

Merged-In: Ide7f60e504c73994ddc6aebf23d2f5c02926d44f
Change-Id: Ide7f60e504c73994ddc6aebf23d2f5c02926d44f
(cherry picked from commit 3b960500)