drm/amdgpu: no rlcg legacy read in SRIOV case

rlcg legacy read is not available in SRIOV configration.
Otherwise, gmc_v9_0_flush_gpu_tlb will always complain
timeout and finally breaks driver load.

v2: bypass read in amdgpu_virt_get_rlcg_reg_access_flag (from Victor)

Fixes: 97d1a3b9 ("drm/amdgpu: switch to get_rlcg_reg_access_flag for gfx9")
Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Victor Skvortsov <Victor.Skvortsov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>