Merge branch 'feature/idf_version' into 'master'

build system: add IDF_VER environment variable and preprocessor define

This adds an `IDF_VER` preprocessor define which is obtained from `git describe`.

Looks like `v1.0-275-g0efaa4f` for non-release version or `v2.0` for a tagged (release) version.

See merge request !403

diff --cc components/bootloader/src/main/bootloader_start.c
index dfcfb0a081fb3fa15b1a1cd0acd8b6b8f00df7bf,102e70c3def7bb8ca6a11f5d5937c185abe5d61a..a374c4306dc22b3c97a94d04814dd5d9f2fbfba9
--- 1/components/bootloader/src/main/bootloader_start.c
--- 2/components/bootloader/src/main/bootloader_start.c
+++ b/components/bootloader/src/main/bootloader_start.c
@@@ -234,15 -232,8 +234,15 @@@ static bool ota_select_valid(const esp_
  
  void bootloader_main()
  {
 +    /* Set CPU to 80MHz.
 +       Start by ensuring it is set to XTAL, as PLL must be off first
 +       (may still be on due to soft reset.)
 +    */
 +    rtc_set_cpu_freq(CPU_XTAL);
 +    rtc_set_cpu_freq(CPU_80M);
 +
      uart_console_configure();
-     ESP_LOGI(TAG, "Espressif ESP32 2nd stage bootloader v. %s", BOOT_VERSION);
+     ESP_LOGI(TAG, "ESP-IDF %s 2nd stage bootloader", IDF_VER);
  #if defined(CONFIG_SECURE_BOOT_ENABLED) || defined(CONFIG_FLASH_ENCRYPTION_ENABLED)
      esp_err_t err;
  #endif

diff --cc make/project.mk
Simple merge