mmc: sdhci-of-arasan: Add DTS property to disable DCMDs.

Direct commands (DCMDs) are an optional feature of eMMC 5.1's command
queue engine (CQE). The Arasan eMMC 5.1 controller uses the CQHCI,
which exposes a control register bit to enable the feature.
The current implementation sets this bit unconditionally.

This patch allows to suppress the feature activation,
by specifying the property disable-cqe-dcmd.

Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Fixes: 84362d7 ("mmc: sdhci-of-arasan: Add CQHCI support for arasan,sdhci-5.1")
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: cmuellner

drivers/mmc/host/sdhci-of-arasan.c

@@ -832,7 +832,10 @@ static int sdhci_arasan_probe(struct platform_device *pdev)
 		host->mmc_host_ops.start_signal_voltage_switch =
 					sdhci_arasan_voltage_switch;
 		sdhci_arasan->has_cqe = true;
-		host->mmc->caps2 |= MMC_CAP2_CQE | MMC_CAP2_CQE_DCMD;
+		host->mmc->caps2 |= MMC_CAP2_CQE;
+
+		if (!of_property_read_bool(np, "disable-cqe-dcmd"))
+			host->mmc->caps2 |= MMC_CAP2_CQE_DCMD;
 	}
 
 	ret = sdhci_arasan_add_host(sdhci_arasan);