drm/amdgpu: Use generic hdp flush function

drm/amdgpu: Use generic hdp flush function

Except HDP v5.2 all use a common logic for HDP flush. Use a generic
function. HDP v5.2 forces NO_KIQ logic, revisit it later.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>