powerpc/mpc85xx: Add workaround for DDR erratum A004508

powerpc/mpc85xx: Add workaround for DDR erratum A004508

When the DDR controller is initialized below a junction temperature of
0°C and then operated above a junction temperature of 65°C, the DDR
controller may cause receive data errors, resulting ECC errors and/or
corrupted data. This erratum applies to the following SoCs and their
variants: MPC8536, MPC8569, MPC8572, P1010, P1020, P1021, P1022, P1023,
P2020.

Signed-off-by: York Sun <yorksun@freescale.com>