drm/amdgpu: Fix memory range calculation

Consider the 16M reserved region also before range calculation for GMC
9.4.3 SOCs.

Fixes: a433f1f5 ("drm/amdgpu: Initialize memory ranges for GC 9.4.3")
Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>