ARM: dts: Add 128MiB OpenBMC flash layout

This is an alternate layout used by OpenBMC systems that require more
space on the BMC's flash. In addition to more space for the rootfs, it
supports a larger u-boot and Linux kernel FIT image.

The division of space is as follows:

 u-boot + env: 1MB
 kernel/FIT: 9MB
 rwfs: 86MB
 rofs: 32MB

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>