[Hexagon] Add support for "new" circular buffer intrinsics

These instructions have been around for a long time, but we
haven't supported intrinsics for them. The "new" vesrions use
the CSx register for the start of the buffer instead of the K
field in the Mx register.

There is a related llvm patch.

Patch by Brendon Cahoon.

llvm-svn: 328725