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: I2ef14204d0db018e7f67578a57e56fdbea8b698c
Change-Id: I2ef14204d0db018e7f67578a57e56fdbea8b698c
(cherry picked from commit 9d95aff9)