drm/amdgpu: skip vram reserve on firmware_v2_2 for bare-metal

vram_usagebyfirmware v2_2 is only used in SRIOV case, skip the related
settings in bare-metal case currently.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>