can: mscan-mpc5xxx: add support for the MPC512x processor

The main differences compared to the MSCAN on the MPC5200 are:

- More flexibility in choosing the CAN source clock and frequency:

  Three different clock sources can be selected: "ip", "ref" or "sys".
  For the latter two, a clock divider can be defined as well. If the
  clock source is not specified by the device tree, we first try to
  find an optimal CAN source clock based on the system clock. If that
  is not possible, the reference clock will be used.

- The behavior of bus-off recovery is configurable:

  To comply with the usual handling of Socket-CAN bus-off recovery,
  "recovery on request" is selected (instead of automatic recovery).

Note that only MPC5121 Rev. 2 and later is supported.

Signed-off-by: Wolfgang Grandegger <wg@denx.de>
Reviewed-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>