When IDF_PATH is not set by the user, cmake infers the same through
other means and sets it as an environment variable. However, some
sub-invocation of cmake may not see this variable as it is not set
in the parent. This change adds a custom command for exporting IDF_PATH
just before invoking ldgen so that IDF_PATH can be used in Kconfig
without any errors.
Added a new structure esp_app_desc_t. It has info about firmware:
version, secure_version, project_name, time/date build and IDF version.
Added the ability to add a custom structure with a description of the firmware.
The esp_app_desc_t is located in fixed place in start of ROM secotor. It is located after structures esp_image_header_t and esp_image_segment_header_t.
app_version is filed from PROJECT_VER variable (if set in custom make file) or PROJECT_PATH/version.txt or git repo (git describe).
Add API to get app_desc from partition.
