[llvm] [offload][openMP] Add __omp_get_device_ptr_if_present api to offload (PR #153146)

[via llvm-commits]

skc7 wrote:

Hi @mjklemm 
I'm re-evaluating if this new utility is actually required. Given a host pointer, making a call to `omp_get_mapped_ptr` from mlir, will do the work for a given valid device number(queried from omp.target) in #140523 
Closing this PR now. Will re-open this if really required.

https://github.com/llvm/llvm-project/pull/153146