[libomptarget][nfc][amdgpu] Remove atmi_status_t type

ATMI_STATUS_UNKNOWN was unused, deleted references to it.
Replaced ATMI_STATUS_{SUCCESS,ERROR} with HSA_STATUS_{SUCCESS,ERROR}
Replaced atmi_status_t with hsa_status_t

Otherwise no change. In particular, conversions between atmi_status_t and
hsa_status_t will now be conversions between hsa_status_t and itself.

Reviewed By: pdhaliwal

Differential Revision: https://reviews.llvm.org/D103115