R600/SI: Use S_LOAD_DWORD instructions for v8i32 and v16i32
R600/SI: Add support for i64 bitwise or
SelectionDAG: Pass along the original argument/element type in ISD::InputArg

For some targets, it is useful to be able to look at the original
type of an argument without having to dig through the original IR.

This also fixes a bug in SelectionDAGBuilder where InputArg.PartOffset
was not taking into account the offset of structure elements.

Patch by: Justin Holewinski

Tom Stellard:
  - Changed the type of ArgVT to EVT, so it can store non-simple types
    like v3i32.
R600: Fix handling of vector kernel arguments

The SelectionDAGBuilder was promoting vector kernel arguments to legal
types, but this won't work for R600 and SI since kernel arguments are
stored in memory and can't be promoted.  In order to handle vector
arguments correctly we need to look at the original types from the LLVM IR
function.