sbc8548: enable ability to boot from alternate flash

This board has an 8MB soldered on flash, and a 64MB SODIMM
flash module.  Normally the board boots from the 8MB flash,
but the hardware can be configured for booting from the 64MB
flash as well by swapping CS0 and CS6.  This can be handy
for recovery purposes, or for supporting u-boot and VxBoot
at the same time.

To support this in u-boot, we need to have different BR0/OR0
and BR6/OR6 settings in place for when the board is configured
in this way, and a different TEXT_BASE needs to be used due
to the larger sector size of the 64MB flash module.

We introduce the suffix _8M and _64M for the BR0/BR6 and the
OR0/OR6 values so it is clear which is being used to map what
specific device.

The larger sector size (512k) of the alternate flash needs
a larger malloc pool, otherwise you'll get failures when
running saveenv, so bump it up accordingly.

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