esp32: Add firmware version to app

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.

components/bootloader_support/include/esp_image_format.h

@@ -89,6 +89,25 @@ typedef struct {
     uint32_t data_len;
 } esp_image_segment_header_t;
 
+#define ESP_APP_DESC_MAGIC_WORD 0xABCD5432 /*!< The magic word for the esp_app_desc structure that is in DROM. */
+
+/**
+ * @brief Description about application.
+ */
+typedef struct {
+    uint32_t magic_word;        /*!< Magic word ESP_APP_DESC_MAGIC_WORD */
+    uint32_t secure_version;    /*!< Secure version */
+    uint32_t reserv1[2];        /*!< --- */
+    char version[32];           /*!< Application version */
+    char project_name[32];      /*!< Project name */
+    char time[16];              /*!< Compile time */
+    char date[16];              /*!< Compile date*/
+    char idf_ver[32];           /*!< Version IDF */
+    uint8_t app_elf_sha256[32]; /*!< sha256 of elf file */
+    uint32_t reserv2[20];       /*!< --- */
+} esp_app_desc_t;
+_Static_assert(sizeof(esp_app_desc_t) == 256, "esp_app_desc_t should be 256 bytes");
+
 #define ESP_IMAGE_MAX_SEGMENTS 16
 
 /* Structure to hold on-flash image metadata */