drm/amdgpu: Rename amdgpu_acpi_is_s0ix_supported

Rename amdgpu_acpi_is_s0ix_supported to better explain
functionality by renaming to amdgpu_acpi_is_s0ix_active

Signed-off-by: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>