Replace deprecated /dev/keychord driver with /dev/input/ interface.
Will restrict which nodes are active and relevant, and try to mask
out any unreferenced inputs with EVIOCSMASK if available.
Test: manual, boot, check registered chord works
Bug: 64114943
Change-Id: I2bbf84a6e472d720f02282e10d56795b75ac62d1
Not just because it's what the cool kids are doing --- it also lets us
simplify the inner loop and decouple it from whatever systems want to
be woken to perform some activity if there's data to be read on some fd.
Currently this is just used to clean up the existing signal handling,
keychord, and property service code.
Change-Id: I4d7541a2c4386957ad877df69e3be08b96a7dec5