drm/amd/pm: Update data types used for uapi i/f

Update member's data type in amdgpu_xcp_metrics from linux specific
to the ones compatible to uapi interface

Fixes: 4c07ff7d ("drm/amd/pm: Add gpu_metrics_v1_6")
Signed-off-by: Asad Kamal <asad.kamal@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>