boot: zephyr: main: fix log_process call after Zephyr change

The legacy logging subsystem was removed in below commit:
https://github.com/zephyrproject-rtos/zephyr/commit/c5f2cde

This commit maintains compatibility with Zephyr upstream before
and after the change by using the now removed CONFIG_LOG1 and
CONFIG_LOG2 defines.

Signed-off-by: Martin Jäger <martin@libre.solar>
diff --git a/boot/zephyr/main.c b/boot/zephyr/main.c
index 3bd8fd3..9d80be5 100644
--- a/boot/zephyr/main.c
+++ b/boot/zephyr/main.c
@@ -327,7 +327,12 @@
     log_init();
 
     while (1) {
+#if defined(CONFIG_LOG1) || defined(CONFIG_LOG2)
+        /* support Zephyr legacy logging implementation before commit c5f2cde */
         if (log_process(false) == false) {
+#else
+        if (log_process() == false) {
+#endif
             if (boot_log_stop) {
                 break;
             }