[media] mt2060: implement sleep

I saw from ZyDAS ZD1301 sniffs it sets chip sleeping by using
REG_MISC_CTRL. That has very huge effect for power management, around
0.9W. Sleep is still disabled for all the old hardware just to avoid
possible regression as meaning of register bits are unknown.

I tested it also with some other devices and it seems to be working,
but I still consider it to be too risky to change it default.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>