mlxsw: reg: Adjust PPCNT register to support local port 255

Local port 255 has a special meaning in PPCNT register, it is used to
refer to all local ports. This wild card ability is not currently used
by the driver.

Special casing local port 255 in Spectrum-4 systems where it is a valid
port is going to be a problem.

Work around this issue by adding and always setting the 'lp_gl' bit
which instructs the device's firmware to treat this local port like an
ordinary port.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>