This patch prevents a tx BD corruption bug by preventing the device from
powering down the PLL from L1 if the link speed is 10Mbps or 100Mbps.

The same bits are also used to prevent a system hang during chip reset
resulting from a complicated set of events that ultimately leads to
PCIe block register corruption.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Reviewed-by: NMichael Chan <mchan@broadcom.com>
Reviewed-by: NBenjamin Li <benli@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>