powerpc/mpc8548: Add workaround for erratum NMG_LBC103

The erratum NMG_LBC103 is LBIU3 in MPC8548 errata document.
Any local bus transaction may fail during LBIU resynchronization
process when the clock divider [CLKDIV] is changing. Ensure there
is no transaction on the local bus for at least 100 microseconds
after changing clock divider LCRR[CLKDIV].

Refer to the erratum LBIU3 of mpc8548.

Signed-off-by: Zhao Chenhui <chenhui.zhao@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>