fix(esp_log): add Kconfig to optionally bypass esp_rom_vprintf

In Log V2, ESP_LOG macros are using the runtime
constrained-environment path in esp_log_vprintf() reference
esp_rom_vprintf as the fallback formatter. On chips where ets_vprintf
is not in ROM (all targets except ESP32-S2 and ESP32-C2), this pulls
~1.2 KB of printf implementation into IRAM.

Add a new Kconfig option LOG_API_CONSTRAINED_ENV_SAFE (default y) that
controls whether this IRAM-resident fallback is used:

Also update the logging and RAM-usage documentation accordingly.

Closes https://github.com/espressif/esp-idf/issues/18346

components/log/include/esp_log_config.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2024-2025 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2024-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -13,6 +13,7 @@
 #include "esp_log_level.h"
 #include "esp_assert.h"
 #include "sdkconfig.h"
+#include "esp_rom_caps.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -111,6 +112,25 @@ extern "C" {
 #ifndef ESP_LOG_FORMATTING_DISABLED
 #define ESP_LOG_FORMATTING_DISABLED              (0)
 #endif
+
+/**
+ * This define controls whether esp_rom_vprintf is used as the fallback print function in constrained
+ * environments (ISR, cache disabled, early startup). When set to 0, esp_rom_vprintf is never referenced,
+ * saving ~1.2 KB of IRAM on chips where it is not a true ROM function.
+ * ESP_DRAM_LOGx and ESP_EARLY_LOGx will use esp_rom_printf directly instead.
+ *
+ * On chips where ets_vprintf is in ROM (ESP32-S2, ESP32-C2), this is always enabled
+ * since there is no IRAM cost.
+ */
+#if BOOTLOADER_BUILD || ESP_ROM_HAS_VPRINTF_FUNC
+#define ESP_LOG_API_CONSTRAINED_ENV_SAFE  (1)
+#else
+#ifdef CONFIG_LOG_API_CONSTRAINED_ENV_SAFE
+#define ESP_LOG_API_CONSTRAINED_ENV_SAFE  (1)
+#else
+#define ESP_LOG_API_CONSTRAINED_ENV_SAFE  (0)
+#endif
+#endif
 /** @endcond */
 
 /**