CSR implementation uses deprecated functions

[powerjg]

When running chisel with the current CSR code we see the following emitted a lot.

litArg is deprecated, use litOption or litTo*Option

This stems from using .asTypeOf to convert from literal to bundle.

#104 gets us partially there, but there's still a few more places we're using .asTypeOf which causes warnings.

For now, I'm going to remove the CSR module from the CPU so we can skip all of these warnings.