drm/amd/amdgpu: Correct VRAM width for APUs with GMC9

DDR4 has a 64-bit width not 128-bits.  It was reporting
twice the width.  Tested with my Ryzen 2400G.
Signed-off-by: NTom St Denis <tom.stdenis@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c

@@ -722,7 +722,10 @@ static int gmc_v9_0_mc_init(struct amdgpu_device *adev)
 		adev->gmc.vram_width = amdgpu_atomfirmware_get_vram_width(adev);
 	if (!adev->gmc.vram_width) {
 		/* hbm memory channel size */
-		chansize = 128;
+		if (adev->flags & AMD_IS_APU)
+			chansize = 64;
+		else
+			chansize = 128;
 
 		tmp = RREG32_SOC15(DF, 0, mmDF_CS_AON0_DramBaseAddress0);
 		tmp &= DF_CS_AON0_DramBaseAddress0__IntLvNumChan_MASK;