net: marvell: prestera: Add router LPM ABI

Add functions to create/delete lpm entry in hw.
prestera_hw_lpm_add() take index of allocated virtual router.
Also it takes grp_id, which is index of allocated nexthop group.
ABI to create nexthop group will be added soon.

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>