net: dsa: bcm_sf2: Unhardcode port numbers

While the current driver mostly supports BCM7445 which has a hardcoded
location for its MoCA port on port 7 and port 0 for its internal PHY,
this is not necessarily true for all other chips out there such as
BCM3390 for instance.

Walk the list of ports from Device Tree, get their port number ("reg"
property), and then parse the "phy-mode" property and initialize two
internal variables: moca_port and a bitmask of internal PHYs. Since we
use interrupts for the MoCA port, we introduce two helper functions to
enable/disable interrupts and do this at the appropriate bank (INTRL2_0
or INTRL2_1).

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>