libril: Add support for ST-Ericsson Thor M7450 modems

The M7450 modem used in the Galaxy Note 4 (N910C variant) uses a libril
implementation similar to the one employed for Intel XMM* modems by Samsung.

This probably needs future adjustments, but so far fixes basic call functions
and signal strength is displayed correctly.

Change-Id: I2d070102ad11746902527da3c2c7f49485c7d7f1