drm/amdgpu/gmc11: fix system aperture set when AGP is enabled

Need to cover both FB and AGP apertures.

v2: fix missed gfxhub_v3_0_3.c

Fixes: c6eafee0 ("Revert "Revert "drm/amdgpu/gmc11: enable AGP aperture""")
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>