zephyr: Get UART console device from devicetree instead of Kconfig.

Updates the Zephyr port to get the UART console device from devicetree
instead of Kconfig. The Kconfig option CONFIG_UART_CONSOLE_ON_DEV_NAME
was removed in Zephyr v2.7.0.

Signed-off-by: Maureen Helm <maureen.helm@intel.com>

ports/zephyr/uart_core.c

@@ -53,10 +53,8 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         }
     }
     #else
-    static const struct device *uart_console_dev;
-    if (uart_console_dev == NULL) {
-        uart_console_dev = device_get_binding(CONFIG_UART_CONSOLE_ON_DEV_NAME);
-    }
+    static const struct device *uart_console_dev =
+        DEVICE_DT_GET(DT_CHOSEN(zephyr_console));
 
     while (len--) {
         uart_poll_out(uart_console_dev, *str++);