dvbsrc: add _MUTABLE_PLAYING to tuning props

The element can (re)tune while playing so basically
every property used at set_fe_params() can be set
in state <= PLAYING.
mpegts: fix typo in GstMpegtsExtendedEventDescriptor doc
dvbsrc: add missing DVB-T2 guard intervals

According to the v4l-dvb API docs, these are only
used for DVB-T2 at the moment.

Order of the enum values (new rates after _AUTO)
has been kept congruent with the one in the v4l
API for consistency.
dvbsrc: add missing DTMB guard intervals
dvbsrc: add missing standard transmission modes

These apply to ISDB-T, DVB-T2 and DTMB

Order of the enum values (new rates after _AUTO)
has been kept congruent with the one in the v4l
API for consistency.
dvbsrc: add preliminary support for DTMB

Previously known as DMB-T/H, this is the
terrestial DTV broadcast standard currently
used by the People's Republic of China,
Hong Kong, Laos and Macau (officially),
and by Malaysia, Iraq, Jordan, Syria and
Lebanon (experimentally).