* Update SPI Engine AD738x
I replaced the SPI Engine connections in the ad738x_bd.tcl with the
spi_engine_create procedure found in the spi_engine.tcl script. Through
these changes, a more generic instantiation for the spi_engine can be
achieved. I changed the ad738x_bd.tcl where it was added spi_engine_create
procedure, system_bd.tcl and system_top.v files.
I have update system_constr.xdc file and added ad738x_fmc.txt file.
Signed-off-by: Ioan-daniel Pop <Pop.Ioan-daniel@analog.com>