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/zephyr/module.yml b/zephyr/module.yml
index 7850f8b..c4293e3 100644
--- a/zephyr/module.yml
+++ b/zephyr/module.yml
@@ -1,2 +1,4 @@
 samples:
   - boot/zephyr
+build:
+  cmake: ./boot/bootutil/zephyr