net: mvpp2: add BM protection underrun feature support

The PP2v23 hardware supports a feature allowing to double the
size of BPPI by decreasing number of pools from 16 to 8.
Increasing of BPPI size protect BM drop from BPPI underrun.
Underrun could occurred due to stress on DDR and as result slow buffer
transition from BPPE to BPPI.
New BPPI threshold recommended by spec is:
BPPI low threshold - 640 buffers
BPPI high threshold - 832 buffers
Supported only in PPv23.

Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Acked-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>