R600: Consolidate expansion of v2i32/v4i32 ops for EG/SI

By default, we expand these operations for both EG and SI. Move the
duplicated code into a common space for now. If the targets ever actually
implement these operations as instructions, we can override that in the relevant
target.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
llvm-svn: 184848