Relocate module Kconfig beneath $module/zephyr/

Separate `boot/zephyr/Kconfig` into the portion to be
picked up through `zephyr/module.yml` (variable declarations)
and the portion appropriate for a top-level Kconfig
(main menu, sourcing Kconfig.zephyr).  Relocate all the
module-specific Kconfig content beneath `$mcuboot/zephyr/`
and extend `$mcuboot/zephyr/module.yml` to reference it.
Fix up mcuboot-specific internal files to get the existing
builds to pass.

Verified by:
1. building with `-t guiconfig` and manually verifying the
   relocation of mcuboot Kconfig content within the Modules:mcuboot
   section.
2. building a full image and verifying the .map file did not change
   in flash or ram size.
3. Further verified that the following testcases still pass with
   mcuboot options on twister:
      mcuboot/boot/zephyr
      zephyr/tests/subsys/dfu
      zephyr/samples/subsys/mgmt/mcumgr/smp_svr

Signed-off-by: Gregory SHUE <[email protected]>

Author: legrand-gregshue

boot/bootutil/zephyr/CMakeLists.txt

@@ -6,7 +6,7 @@ if(CONFIG_MCUBOOT_BOOTUTIL_LIB)
 
 zephyr_interface_library_named(MCUBOOT_BOOTUTIL)
 
-target_include_directories(MCUBOOT_BOOTUTIL INTERFACE
+zephyr_include_directories(MCUBOOT_BOOTUTIL INTERFACE
   ../
   ../include
   ../../zephyr/include