Add functions and structures to allocate virtual router.
prestera_hw_vr_create() return index of allocated VR so that we can move
forward and also add another objects (e.g. router interface),
which has link to VR.
Co-developed-by: Taras Chornyi <tchornyi@marvell.com> Signed-off-by: Taras Chornyi <tchornyi@marvell.com> Co-developed-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu> Signed-off-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu> Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu> Signed-off-by: David S. Miller <davem@davemloft.net>