[PATCH] media: add Analog Devices ADV7393 video encoder driver

Add ADV7393 I²C-based video encoder driver. This driver has been tested on
custom hardware. It has been tested for composite output. It is derived from the
ADV7343 driver.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>