[Offload] Use the kernel argument size directly in AMDGPU offloading (#94667)

Summary:
The old COV3 implementation of HSA used to omit the implicit arguments
from the kernel argument size. For COV4 and COV5 this is no longer the
case so we can simply use the size reported from the symbol information.

See
https://github.com/ROCm/ROCR-Runtime/issues/117#issuecomment-812758161