drm/amdgpu: Don't flush/invalidate HDP for APUs and A+A

Integrate two generic functions to determine if HDP
flush is needed for all Asics.

Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>