mimxrt1050: check if D-cache is enabled before enabling it.

An issue has been confirmed in CMSIS core header file in
SCB_EnableDCache when stack is in cacheable memory.

Issue report: ARM-software/CMSIS_5#331

To workaround this issue by checking if Dcache's been enabled before
trying to enable it.

Signed-off-by: Ryan QIAN <jianghao.qian@nxp.com>

arch/arm/soc/nxp_imx/rt/soc.c

@@ -131,7 +131,9 @@ static int imxrt_init(struct device *arg)
 	}
 
 	SCB_EnableICache();
-	SCB_EnableDCache();
+	if (!(SCB->CCR & SCB_CCR_DC_Msk)) {
+		SCB_EnableDCache();
+	}
 
 	_ClearFaults();