drm/amdgpu: exclude duplicate pages from UMC RAS UE count

If a UMC bad page is reserved but not freed by an application, the
application may trigger uncorrectable error repeatly by accessing the page.

v2: add specific function to do the check.
v3: remove duplicate pages, calculate new added bad page number.
v4: reuse save_bad_pages to calculate new added bad page number.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Stanley.Yang <Stanley.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>