zephyr: Update to new zephyr timeout API.

Updates the zephyr port to use the new timeout api introduced in zephyr
2.3.

ports/zephyr/mphalport.h

@@ -21,7 +21,7 @@ static inline void mp_hal_delay_us(mp_uint_t delay) {
 }
 
 static inline void mp_hal_delay_ms(mp_uint_t delay) {
-    k_sleep(delay);
+    k_msleep(delay);
 }
 
 #define mp_hal_delay_us_fast(us)   (mp_hal_delay_us(us))

ports/zephyr/uart_core.c

@@ -49,7 +49,7 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     while (len--) {
         char c = *str++;
         while (console_putchar(c) == -1) {
-            k_sleep(1);
+            k_msleep(1);
         }
     }
     #else