dt-bindings: mmc: sdhci-am654: Add flag to force setting of TESTCD bit

The ARASAN MMC controller on Keystone 3 class of devices needs the SDCD
line to be connected for proper functioning. Similar to the issue pointed
out in sdhci-of-arasan.c driver, commit 3794c542 ("mmc:
sdhci-of-arasan: Set controller to test mode when no CD bit").

In cases where SDCD line is not connected, adding
"ti,fails-without-test-cd" in the DT node helps to indicate the
controller, that the SDCD line has been pulled down, using the TESTCD bit.
Signed-off-by: NAswath Govindraju <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20220425063120.10135-2-a-govindraju@ti.comSigned-off-by: NUlf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/sdhci-am654.yaml

@@ -186,6 +186,13 @@ properties:
     description: Clock Delay Buffer Select
     $ref: "/schemas/types.yaml#/definitions/uint32"
 
+  ti,fails-without-test-cd:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description:
+      When present, indicates that the CD line is not connected
+      and the controller is required to be forced into Test mode
+      to set the TESTCD bit.
+
 required:
   - compatible
   - reg