devices.cpp handles too many things for creating one class. This
change breaks it up into various files and classes.
* Parsing is moved to ueventd_parser.cpp
* Reading from the uevent socket and Cold booting is moved to a
UeventListener class, in uevent_listener.cpp
* Firmware handling is moved to firmware_handler.cpp
* The remaining contents form a DeviceHandler class within devices.cpp
Bug: 33785894
Test: boot bullhead x40, observe no major differences in /dev and /sys
Test: boot sailfish x40, observe no major differences in /dev and /sys
Test: init unit tests
Change-Id: I846a2e5995fbb344c7a8e349065c18a934fa6aba
