powerpc/44x: Correct memory size calculation for denali-based boards

Some U-Boot versions incorrectly set the number of chipselects to two
for Sequoia/Rainier boards while they only have one chipselect hardwired.
This patch adds a workaround for this, hardcoding the number of chipselects
to one for sequioa/rainer board models and reading the actual value from
the memory controller register DDR0_10 otherwise.

It also fixes another error in the way ibm4xx_denali_fixup_memsize
calculates memory size. When testing the DDR_REDUC bit, the polarity is
backwards.  A "1" implies 32-bit wide memory while a "0" implies 64-bit
wide memory.

Signed-off-by: Mikhail Zolotaryov <lebon@lebon.org.ua>
Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
Signed-off-by: Steven A. Falco <sfalco@harris.com>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>