drm/amdgpu: rename amdgpu_vm_update_params

Well those are actually page table entry parameters.
This also makes the variable names used a bit shorter.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>