drm/amdgpu/discovery: refactor ip list traversal

for each ip, check whether it is needed by amdgpu driver,
if yes, record its base addresses

v2: change some DRM_INFO to DRM_DEBUG
v3: remove unused variable (Alex)

Signed-off-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>