MCUXpresso: Change the MXRT deep sleep implementation

The code checks if any of the UART's is still transmitting.
If so then prevent from entering deepsleep

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>

Author: mmahadevan108

targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_IMX/sleep.c

@@ -19,8 +19,7 @@
 
 extern void vPortPRE_SLEEP_PROCESSING(clock_mode_t powermode);
 extern void vPortPOST_SLEEP_PROCESSING(clock_mode_t powermode);
-extern void serial_wait_tx_complete(uint32_t uart_index);
-
+extern bool serial_check_tx_ongoing();
 
 void hal_sleep(void)
 {
@@ -35,10 +34,12 @@ void hal_sleep(void)
 
 void hal_deepsleep(void)
 {
-    vPortPRE_SLEEP_PROCESSING(kCLOCK_ModeStop);
+    /* Check if any of the UART's is transmitting data */
+    if (serial_check_tx_ongoing()) {
+        return;
+    }
 
-    /* Wait till debug UART is done transmitting */
-    serial_wait_tx_complete(STDIO_UART);
+    vPortPRE_SLEEP_PROCESSING(kCLOCK_ModeStop);
 
     __DSB();
     __WFI();