boot: zephyr: migrate to new log subystem

The old log subsystem has been deprecated in Zephyr.
Migrate to the new subsystem to avoid compilation warnings.

In-place log processing is selected as it is required as MCUBoot is
one thread application.

Signed-off-by: Emanuele Di Santo <emdi@nordicsemi.no>
Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/zephyr/main.c b/boot/zephyr/main.c
index 345b449..f4bc4ab 100644
--- a/boot/zephyr/main.c
+++ b/boot/zephyr/main.c
@@ -40,6 +40,8 @@
 };
 #endif
 
+MCUBOOT_LOG_MODULE_REGISTER(mcuboot);
+
 void os_heap_init(void);
 
 #if defined(CONFIG_ARM)