bootutil: Move state-independent area APIs

Move functions, that operate on the flash area and does not require the
bootloader state or bootloader status into a separate, dedicated file.

Signed-off-by: Tomasz Chyrowicz <tomasz.chyrowicz@nordicsemi.no>

Author: tomchy

boot/bootutil/CMakeLists.txt

@@ -21,6 +21,7 @@ target_sources(bootutil
         src/bootutil_img_hash.c
         src/bootutil_img_security_cnt.c
         src/bootutil_misc.c
+        src/bootutil_area.c
         src/bootutil_public.c
         src/caps.c
         src/encrypted.c