Enhance detection of evdev nodes that report double tap as power key

Jolla phone reports double taps as power key events and thus mce needs
to be able to tell apart the real power key button from the powerkey
events generated due to double tap.

If mce makes a wrong guess here, the power button can't be used to
a) turn on the display when proximity is covered
b) turn off the display
c) power off the device via long power key press

To make false positives less likely, the input device must now be exactly
like the one in Jolla phone before it gets treated as double tap device.

[mce] Enhance detection of evdev nodes that report double tap as power key
Merge pull request #131 from spiiroin/powerkey_or_doubletap

Enhance detection of evdev nodes that report double tap as power key