bootloader: Enable early boot RNG entropy source

This reverts commit ceb8566970.

components/bootloader_support/include_priv/bootloader_random.h

@@ -16,6 +16,30 @@
 
 #include <stddef.h>
 
+/**
+ * @brief Enable early entropy source for RNG
+ *
+ * Uses the SAR ADC to feed entropy into the HWRNG. The ADC is put
+ * into a test mode that reads the 1.1V internal reference source and
+ * feeds the LSB of data into the HWRNG.
+ *
+ * Can also be used from app code early during operation, if entropy
+ * is required before WiFi stack is initialised. Call this function
+ * from app code only if WiFi/BT are not yet enabled and I2S and SAR
+ * ADC are not in use.
+ *
+ * Call bootloader_random_disable() when done.
+ */
+void bootloader_random_enable(void);
+
+/**
+ * @brief Disable early entropy source for RNG
+ *
+ * Disables SAR ADC source and resets the I2S hardware.
+ *
+ */
+void bootloader_random_disable(void);
+
 /**
  * @brief Fill buffer with 'length' random bytes
  *