drm/amd: Convert amdgpu to use suballocation helper.

Now that we have a generic suballocation helper, Use it in amdgpu.
For lines that get moved or changed, also fix up pre-existing style issues.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Co-developed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230224095152.30134-3-thomas.hellstrom@linux.intel.com