bootutil: extracted app common library from bootutil_misc

Part of code of boot/bootutil/ is re-implemented in zephyr-rtos
repository.
As some code are defined here and there it becomes problem when
need to include it with outstanding feature in a build.
It is possible to mitigate problem using #fdefry - but this was
rather temporary hack.

This patch introduce new module which is common for MCUBoot build
and application build.
Common code were extracted to bootutil_public.c source file and
bootutil_public.h header

MCUboot also select DISABLE_MCUBOOT_BOOTUTIL_LIB_OWN_LOG Kconfig
option, as it must define log configuration on its own for all its
sourcecode.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 0d0bed3..ef3e834 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -14,6 +14,7 @@
 	bool
 	select MPU_ALLOW_FLASH_WRITE if ARM_MPU
 	select USE_DT_CODE_PARTITION if HAS_FLASH_LOAD_OFFSET
+	select MCUBOOT_BOOTUTIL_LIB
 
 config BOOT_USE_MBEDTLS
 	bool
@@ -573,4 +574,9 @@
 config USB_DEVICE_PRODUCT
 	default "MCUBOOT"
 
+# use MCUboot's own log configuration
+config MCUBOOT_BOOTUTIL_LIB_OWN_LOG
+	bool
+	default n
+
 source "Kconfig.zephyr"