v4l2-sysfs-path: print the subdevs associated with that device

v4l2-sysfs-path: print the subdevs associated with that device

From: Mauro Carvalho Chehab <mchehab@redhat.com>

The sysfs interface stores links to the other devices associated with a
V4L link.

Improves this util to display those associated subdevices. This small
tool can be used inside other V4L applications to properly associate
audio, input, sound and dvb devices with a /dev/video? file.

device     = /dev/video0
bus info   = usb-0000:00:1d.7-8
sysfs path = /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-8
Subdevs: usb_endpoint:usbdev1.8_ep00 i2c-adapter:i2c-4 input:input8
sound:pcmC1D0c sound:dsp1 sound:audio1 sound:controlC1 sound:mixer1
dvb:dvb0.frontend0 dvb:dvb0.demux0 dvb:dvb0.dvr0 dvb:dvb0.net0

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