drm/amdgpu: add UMA allocation setting helpers

drm/amdgpu: add UMA allocation setting helpers

On some platforms, UMA allocation size can be set using the ATCS
methods. Add helper functions to interact with this functionality.

Co-developed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Yo-Jung Leo Lin (AMD) <Leo.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>