drm/amdgpu/display: fix build error casused by CONFIG_DRM_AMD_DC_DCN2_1

when CONFIG_DRM_AMD_DC_DCN2_1 is not enable in .config,
there is build error. struct dpm_clocks shoud not be
guarded.

Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Reviewed-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>