[$] Initializing the entropy pool using RDRAND and friends

<p>Random number generation in the kernel has garnered a lot of attention overthe years. The tensions between the need for cryptographic-strength randomnumbers versus getting strong random numbers more quickly-along with the needto avoid regressions-has led to something of a patchwork of APIs. While itis widely agreed that waiting for a properly initialized random numbergenerator (RNG) before producing random numbers is the proper course,opinions differ on what "properly" means exactly. Beyond that, waiting,especially early in the boot process, can be problematic as well. Onesolution would be to trust the RNG instructions provided by most modernprocessors, but that comes with worries of its own.