drm/amdgpu: Update invalidate and flush hdp function

drm/amdgpu: Update invalidate and flush hdp function

Update asic_invalidate_hdp and asic_flush_hdp function to check if ip
function exist, if not return void

v2: Use else/if (Kevin)
    Update function name (Lijo)

Signed-off-by: Asad Kamal <asad.kamal@amd.com>
Suggested-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>