random: add back async readiness notifier

This is required by vsprint, because it can't do things synchronously
from hardirq context, and it will be useful for an EFI notifier as well.
I didn't initially want to do this, but with two potential consumers
now, it seems worth it.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
2 files changed