add amdgpu_acpi_is_s0ix_supported() to check the platform
whether support s0i3.

v2: fix empty function parameters warning (void)
Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>