random: document add_hwgenerator_randomness() with other input functions

 *                                unsigned int value);

 *	void add_interrupt_randomness(int irq, int irq_flags);

 * 	void add_disk_randomness(struct gendisk *disk);

 *	void add_hwgenerator_randomness(const char *buffer, size_t count,

 *					size_t entropy);

 *	void add_bootloader_randomness(const void *buf, unsigned int size);

 *

 * add_device_randomness() is for adding data to the random pool that

 * is likely to differ between two devices (or possibly even per boot).

 * particular randomness source.  They do this by keeping track of the

 * first and second order deltas of the event timings.

 *

 * add_hwgenerator_randomness() is for true hardware RNGs, and will credit

 * entropy as specified by the caller. If the entropy pool is full it will

 * block until more entropy is needed.

 *

 * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or

 * add_device_randomness(), depending on whether or not the configuration

 * option CONFIG_RANDOM_TRUST_BOOTLOADER is set.

 *

 * Ensuring unpredictability at system startup

 * ============================================

 *