net: mvpp2: adapt the mvpp2_rxq_*_pool_set functions to PPv2.2

The MVPP2_RXQ_CONFIG_REG register has a slightly different layout
between PPv2.1 and PPv2.2, so this commit adapts the functions modifying
this register to accommodate for both the PPv2.1 and PPv2.2 cases.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>