drm/amdgpu: fix AGP init order

drm/amdgpu: fix AGP init order

The default AGP settings were overwriting the IP selected
ones since the default was getting set after the IP ones
were selected.

Fixes: de59b69932e6 ("drm/amdgpu/gmc: set a default disable value for AGP")
Link: https://lists.freedesktop.org/archives/amd-gfx/2023-November/100966.html
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>