drm/amdgpu: invoke req full access early enough

From SIENNA_CICHLID, HW introduce a new protection
feature which can control the FB, doorbell and MMIO
write access for VF, so guest driver should request
full access before ip discovery, or we couldn't access
ip discovery data in FB.

Signed-off-by: Wenhui Sheng <Wenhui.Sheng@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>