include: Add functions needed by MTK driver

Due to the way the current MTK device plugin handles creation of
atoms, some modem state transitions cannot be handled directly by
the core. This change adds a new function that can be used by a
device plugin to prevent the modem core code from setting the modem
state to PRE-SIM when a SIM lock condition is detected.
src: Implement functions needed by MTK driver

Due to the way the current MTK device plugin handles creation of
atoms, some modem state transitions cannot be handled directly by
the core. This change adds a new function that can be used by a
device plugin to prevent the modem core code from setting the modem
state to PRE-SIM when a SIM lock condition is detected.
mtk: Handle locking of the SIM

Atoms are destroyed when the SIM gets locked after introduction of
wrong password.
src: Check presence of spn_watches on removal

In some cases sim->spn_watches can already be NULL when trying to
remove the watches.
Merge pull request #118 from alfonsosanchezbeato/puk-locked-crash

Fix crash when the modem gets PUK locked