dt: sdhci-of-arasan: Add device tree option xlnx, fails-without-test-cd

The sdhci controller on xilinx zynq devices will not function unless
the CD bit is provided. http://www.xilinx.com/support/answers/61064.html


In cases where it is impossible to provide the CD bit in hardware,
setting the controller to test mode and then setting inserted to true
will get the controller to function without the CD bit.

The device property "xlnx,fails-without-test-cd" will let the arasan
driver know the controller does not have the CD line wired and that the
controller does not function without it.

Signed-off-by: Zach Brown <zach.brown@ni.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>