drm/amdgpu: equip new req_init_data handshake

by this new handshake host side can prepare vbios/ip-discovery
and pf&vf exchange data upon recieving this request without
stopping world switch.

this way the world switch is less impacted by VF's exclusive mode
request

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>