cmake: fix custom bootloader issue

Issue is that when users creates a custom bootloader from
$IDF_PATH/components/bootloader. Parent project build uses the copy but
bootloader subproject build uses the original still. The issue is solved
by passing the custom bootloader as extra component directory so
bootloader build knows to use the new copy (itself) in the build.

components/bootloader/project_include.cmake

@@ -15,9 +15,10 @@ set(bootloader_binary_files
 
 externalproject_add(bootloader
     # TODO: support overriding the bootloader in COMPONENT_PATHS
-    SOURCE_DIR "${IDF_PATH}/components/bootloader/subproject"
+    SOURCE_DIR "${CMAKE_CURRENT_LIST_DIR}/subproject"
     BINARY_DIR "${bootloader_build_dir}"
     CMAKE_ARGS  -DSDKCONFIG=${SDKCONFIG} -DIDF_PATH=${IDF_PATH}
+                -DEXTRA_COMPONENT_DIRS=${CMAKE_CURRENT_LIST_DIR}
     INSTALL_COMMAND ""
     BUILD_ALWAYS 1  # no easy way around this...
     BUILD_BYPRODUCTS ${bootloader_binary_files}