Adds DVBv5 stats support. For now, just mimic whatever dib8000
does, as they're very similar, with regards to statistics.

However, dib7000p_get_time_us() likely require some
adjustments, as I didn't actually reviewed the formula
for it to work with DVB-T. Still, better than nothing,
as latter patches can improve it.

This patch also doesn't show the signal strength in dB
yet. The code is already there, but it requires to be
callibrated.

A latter patch will do the calibration.

It seems that this patch is also a bug fix: Before this
patch, the frontend were not tuning with some userspace
tools. I suspect that dib7000p firmware or hardware
internally expects that the statistics to be collected,
in order for it to work. With this patch, the DVB core
will always retrive statistics, even if userspace doesn't
request. So, it makes the device work on all tested apps.
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>