Hardware RNG on ARM

[Sainan]

There's the following optional registers:

• https://developer.arm.com/documentation/ddi0601/2022-12/AArch64-Registers/RNDR--Random-Number (RDRAND equivalent)
• https://developer.arm.com/documentation/ddi0601/2022-12/AArch64-Registers/RNDRRS--Reseeded-Random-Number (RDSEED equivalent)

Bitcoin Core's implementation for reference:

• https://github.com/bitcoin/bitcoin/blob/master/src/random.h
• https://github.com/bitcoin/bitcoin/blob/master/src/random.cpp

In terms of support, it seems like the Snapdragon X Elite is the only consumer chip that supports this right now. There's also no feature check for this on Windows yet, so might still be a while until this really makes sense.