drm/amdgpu: increase atombios cmd timeout

mitigates race condition on BACO reset between GPU bootcode and driver reload

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>