[media] CXD2820R: Replace i2c message translation with repeater gate control

This patch implements an i2c_gate_ctrl op for the cxd2820r. Thanks to Robert
Schlabbach for identifying the register address and field to set.

The old i2c intercept code that prefixed messages with a passthrough byte has
been removed and the PCTV nanoStick T2 290e entry in em28xx-dvb has been
updated appropriately.

Tested for DVB-T2 use; I would appreciate it if somebody with DVB-C capabilities
could test it as well - from inspection I cannot see any problems.

This is patch v2. It fixes some schoolboy style errors and removes superfluous
i2c entries in cxd2820r.h.

Signed-off-by: Steve Kerrison <steve@stevekerrison.com>
Acked-by: Antti Palosaari <crope@iki.fi>
Tested-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>