radv: setup llvm target data layout

radv: setup llvm target data layout

Ported from radeonsi, pointed out by Tom.

"This prevents LLVM from using sext instructions for local memory
offsets and allows the backend to fold immediate offsets into the
instruction. This also prevents some incorrect code generation for
ptrtoint and inttoptr instructions."

Cc: "13.0 17.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Tom Stellard <tstellar@redhat.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Dave Airlie <airlied@redhat.com>