lima/ppir: implement discard and discard_if
Implement discard and discard_if intrinsics.
This commit also adds codegen for branch since we need it for discard_if. Currently branch implementation is naive and just compares condition with 0.
Since 2 intrinsics may not have explicit dependencies (e.g. branch_if; store_output) this change adds fake dependencies to preserve instruction order.
Signed-off-by: Vasily Khoruzhick anarsoul@gmail.com