This patch updates Flang lowering and kernel flags identification in
MLIR so that loop bounds on `target teams loop` constructs are evaluated
on the host, making the trip count available to the corresponding
`__tgt_target_kernel` call emitted for the target region.
This is necessary in order to properly execute these constructs as
`target teams distribute parallel do`.
Co-authored-by: Kareem Ergawy <kareem.ergawy@amd.com>