[media] Remove the remaining usages for T_STANDBY

tda9887 used to use the T_STANDBY type internally, while tea5761
used it to put the device to sleep. Fix the code for it to work
properly with the tuner core changes and remove this flag from
tuner.h.

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