gril: Add screen state request

This request informs ril of the current screen state.
rilmodem: Move radio settings defs to header

Move some function and struct definitions so we can re-use them for
mtkmodem driver.
mtkmodem: Create fast dormancy request

This request sets fast dormancy and its parameters.
mtkmodem: Add radio settings atom

This atom is needed as the way to set low power mode requires an
additional request.
build: Add mtkmodem radio settings atom
mtk: Use specific driver for radio settings
unit: Add screen state request tests
Merge pull request #91 from alfonsosanchezbeato/lowpowermode

Low power mode