random pt3: More core and accounting cleanups

This is a third series of various cleanups for drivers/char/random.c. It applies on top of the previous 10.

These bits greatly simplify the setup:

1  More meaningful pool names
2  Static allocation of pools
3  Static sysctl bits

These bits make the accounting safer and the code easier to follow:

4  Catastrophic reseed checks
5  Entropy reservation accounting
6  Reservation flag in pool struct
7  Reseed pointer in pool struct
8  Break up extract_user

These bits clean up the hashing functions:
9 Remove dead MD5 copy
10 Simplify hash folding
11 Clean up hash buffering

This bit drops a bunch of code and reduces lock hold times:
12 Remove entropy batching

The next series focuses on moving and sharing code more appropriately.