vcom5s: implement finger detection
vcom5s: implement finger detection

Uses thresholding of average pixel intensity of the center region of
the image.

Also document guessed meanings of magic numbers for registers.

jipumarino/libfprint,micw/libfprint,kunalg/libfprint,dsd/libfprint,abhishekgahlot/fprint-bsapi,abhishekgahlot/fprint-bsapi,sbambrough/libfprint_extended,zemen/libfprint,jipumarino/libfprint,FabriceSalvaire/libfprint-baspi,yingted/etes603,Gnate/libfprint,abhishekgahlot/libfprint,abhishekgahlot/fprint-bsapi,anarsoul/libfprint,dsd/libfprint,iafilatov/libfprint,jipumarino/libfprint,yingted/etes603,payden/libfprint,sbambrough/libfprint_extended,payden/libfprint,hyperair/fprint-bsapi,kunalg/libfprint,freedesktop-unofficial-mirror/libfprint__libfprint,hyperair/fprint-bsapi,ccsystems/libfprint,payden/libfprint,abhishekgahlot/libfprint,zOrg1331/libfprint,PDXostc/libfprint,yingted/etes603,bhdn/libfprint-vkapi,Gnate/libfprint,FabriceSalvaire/libfprint-baspi,hyperair/fprint-bsapi,FabriceSalvaire/libfprint-baspi,PDXostc/libfprint,PDXostc/libfprint,kunalg/libfprint,ccsystems/libfprint,Gnate/libfprint,rmarku/libfprint,zemen/libfprint,zemen/libfprint,bhdn/libfprint-vkapi,zOrg1331/libfprint,zOrg1331/libfprint,rmarku/libfprint,rmarku/libfprint,abhishekgahlot/libfprint,anarsoul/libfprint,freedesktop-unofficial-mirror/libfprint__libfprint,freedesktop-unofficial-mirror/libfprint__libfprint,ccsystems/libfprint,micw/libfprint,bhdn/libfprint-vkapi,micw/libfprint,sbambrough/libfprint_extended