zephyr: add default LOG and MULTITHREADING values in kconfig

Add Log processing configuration synchronous as default
if multithreading is disabled.

Additionally Kconfig makes MULTITHREADING default
if USB is selected.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index dacaf3a..d8f72a3 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -353,9 +353,13 @@
 # it to n here. Otherwise, having it on by default makes the most
 # hardware work.
 config MULTITHREADING
+	default y if BOOT_SERIAL_CDC_ACM #usb driver requires MULTITHREADING
 	default n if SOC_FAMILY_NRF
 	default y
 
+config LOG_IMMEDIATE
+	default n if MULTITHREADING
+
 config UPDATEABLE_IMAGE_NUMBER
 	int "Number of updateable images"
 	default 1