drm: xlnx: sdi: Adding sdi-tx driver

drm: xlnx: sdi: Adding sdi-tx driver

Adding sdi transmitter subsystem driver
SDI transmitter subsystem implements a SDI transmit interface in
accordance to the serial digital interface (SDI) family of standards.
The subsystem accepts video from AXI-4 Stream Video interface and outputs
Native Video stream, and allows for fast selection of the top-level
parameters and automates most of the lower level parameterization. The
AXI4-Stream video interface allows a seamless interface to other
AXI4-Stream-based subsystems.

Signed-off-by: Saurabh Sengar <saurabhs@xilinx.com>
Reviewed-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>