MLK-20440 dts: ecspi: Add ecspi and its slave dts files for imx6ul

MLK-20440 dts: ecspi: Add ecspi and its slave dts files for imx6ul

For ECSPI test, add these two dts files.
imx6ul-14x14-evk-ecspi.dts: enable ecspi4 function. Because ethernet2
uses the same pins with ecspi4, so disable fec1/fec2.
imx6ul-14x14-evk-ecspi-slave.dts: Add "spi-slave" attribute to enable
slave mode.

Wire Connection:
J1704:
	3 - SCS
	4 - MOSI
	5 - MISO
	6 - SCK
	7 - GND

Modify "Makefile" to build these two dts files.

Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Signed-off-by: Arulpandiyan Vadivel <arulpandiyan_vadivel@mentor.com>