ir-keytable: Get decoder capabilities from sysfs

ir-keytable: Get decoder capabilities from sysfs

It will now show also the supported/current protocols, and identify
if the RC has a hardware or a software decoder:

Found /sys/class/rc/rc0/ (/dev/input/event8) with:
        Driver "saa7134", raw software decoder, table "rc-avermedia-m135a-rm-jx"
        Supported protocols: NEC RC-5 RC-6
Found /sys/class/rc/rc1/ (/dev/input/event9) with:
        Driver "cx88xx", hardware decoder, table "rc-pixelview-mk12"
        Supported protocols: other
        Current protocols: NEC
Found /sys/class/rc/rc2/ (/dev/input/event10) with:
        Driver "em28xx", hardware decoder, table "rc-rc5-hauppauge-new"
        Supported protocols: NEC RC-5
        Current protocols: RC-5

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>