MTK SIM hot swap

This PR re-starts the modem after receiving MTK specific events for SIM insertion or removal. MTK, differently from mako, does not receive RIL_UNSOL_RESPONSE_SIM_STATUS_CHANGED events when that happens, but its own proprietary events. Additionally, due to the way mtk has to handle ofono modem states, these events are handled directly in the mtk plugin instead of in the sim atom.

The changes actually provide full hot SIM swap, as ofono is fully functional after the insertion/removal of the SIM. However, the detection of the SIM insertion/removal from ofono users might need to be handled differently to the mako case, as changes to "Present" property are not signalled. The user can look for changes in "Features" property instead, for instance.