[X86] Added missing RCL/RCR schedule overrides to the generic SNB model

The SandyBridge model was missing schedule values for the RCL/RCR values - instead using the (incredibly optimistic) WriteShift (now WriteRotate) defaults.

I've added overrides with more realistic (slow) values, based on a mixture of Agner/instlatx64 numbers and what later Intel models do as well.

This is necessary to allow WriteRotate to be updated to remove other rotate overrides.

It'd probably be a good idea to investigate a WriteRotateCarry class at some point but its not high priority given the unusualness of these instructions.

llvm-svn: 342842