zephyr/uart_core: Access console UART directly instead of printk() hack.

This is required to avoid extra level of output "cooking" ("\r\r\n") and
make test infrastructure work. On the other hand, this breaks somewhat
Zephyr console abstraction.

zephyr/uart_core.c

@@ -26,9 +26,8 @@
 #include <unistd.h>
 #include "py/mpconfig.h"
 #include "src/zephyr_getchar.h"
-
-// Stopgap
-extern void printk(const char*, ...);
+// Zephyr headers
+#include <uart.h>
 
 /*
  * Core UART functions to implement for a port
@@ -41,7 +40,12 @@ int mp_hal_stdin_rx_chr(void) {
 
 // Send string of given length
 void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+    static struct device *uart_console_dev;
+    if (uart_console_dev == NULL) {
+        uart_console_dev = device_get_binding(CONFIG_UART_CONSOLE_ON_DEV_NAME);
+    }
+
     while (len--) {
-        printk("%c", *str++);
+        uart_poll_out(uart_console_dev, *str++);
     }
 }