drm/amdgpu: postpone entering fullaccess mode

if host support new handshake we only need to enter
fullaccess_mode in ip_init() part, otherwise we need
to do it before reading vbios (becuase host prepares vbios
for VF only after received REQ_GPU_INIT event under
legacy handshake)

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>