radeon/llvm: use bitcasts for integers

radeon/llvm: use bitcasts for integers

We're using float as default type, so basically for every instruction that
wants other types for dst/src operands we need to perform the bitcast
to/from default float. Currently bitcast produces no-op MOV instruction,
will be eliminated later.

Signed-off-by: Vadim Girlin <vadimgirlin@gmail.com>