drm/amd/display: fix the white screen issue when >= 64GB DRAM

Dropping bit 31:4 of page table base is wrong, it makes page table
base points to wrong address if phys addr is beyond 64GB; dropping
page_table_start/end bit 31:4 is unnecessary since dcn20_vmid_setup
will do that. Also, while we are at it, cleanup the assignments using
upper_32_bits()/lower_32_bits() and AMDGPU_GPU_PAGE_SHIFT.

Cc: stable@vger.kernel.org
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2354
Fixes: 81d0bcf9 ("drm/amdgpu: make display pinning more flexible (v2)")
Acked-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Co-developed-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1283,11 +1283,15 @@ static void mmhub_read_system_context(struct amdgpu_device *adev, struct dc_phy_
 
 	pt_base = amdgpu_gmc_pd_addr(adev->gart.bo);
 
-	page_table_start.high_part = (u32)(adev->gmc.gart_start >> 44) & 0xF;
-	page_table_start.low_part = (u32)(adev->gmc.gart_start >> 12);
-	page_table_end.high_part = (u32)(adev->gmc.gart_end >> 44) & 0xF;
-	page_table_end.low_part = (u32)(adev->gmc.gart_end >> 12);
-	page_table_base.high_part = upper_32_bits(pt_base) & 0xF;
+	page_table_start.high_part = upper_32_bits(adev->gmc.gart_start >>
+						   AMDGPU_GPU_PAGE_SHIFT);
+	page_table_start.low_part = lower_32_bits(adev->gmc.gart_start >>
+						  AMDGPU_GPU_PAGE_SHIFT);
+	page_table_end.high_part = upper_32_bits(adev->gmc.gart_end >>
+						 AMDGPU_GPU_PAGE_SHIFT);
+	page_table_end.low_part = lower_32_bits(adev->gmc.gart_end >>
+						AMDGPU_GPU_PAGE_SHIFT);
+	page_table_base.high_part = upper_32_bits(pt_base);
 	page_table_base.low_part = lower_32_bits(pt_base);
 
 	pa_config->system_aperture.start_addr = (uint64_t)logical_addr_low << 18;