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/serial_adapter.c b/boot/zephyr/serial_adapter.c
index fc39f71..14adb45 100644
--- a/boot/zephyr/serial_adapter.c
+++ b/boot/zephyr/serial_adapter.c
@@ -25,6 +25,8 @@
 #error Zephyr UART console must been disabled if serial_adapter module is used.
 #endif
 
+MCUBOOT_LOG_MODULE_REGISTER(serial_adapter);
+
 /** @brief Console input representation
  *
  * This struct is used to represent an input line from a serial interface.