[media] em28xx: PCTV tripleStick (292e) LNA support

External LNA between antenna connector and RF tuner is controlled
by EM28178 GPIO 0. GPIO value 1 is LNA active and value 0 is LNA
disabled.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>