sbc8548: Fix up local bus init to be frequency aware

sbc8548: Fix up local bus init to be frequency aware

The code here was copied from the mpc8548cds support, and it
wasn't using the CONFIG_SYS_LBC_LCRR define, and was just
unconditionally setting the LCRR_EADC bit.  Snooping with a
hardware debugger also showed we had LCRR_DBYP set, since we were
setting it based on a read of an uninitialized lcrr read via
clkdiv.  Borrow from the code in the tqm85xx.c support to add
LBC frequency aware masking of these bits.

This change will correct reliability issues associated with trying
to use the 128MB of LBC 100MHz SDRAM on this board.  Thanks to
Keith Savage for assistance in diagnosing the root cause of this.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>