ARM: dts: Add 64MiB OpenBMC flash layout

This is an alternate layout used by OpenBMC systems

The division of space is as follows:

 u-boot + env: 0.5MB
 kernel/FIT: 5MB
 rofs: 42.5MB
 rwfs: 16MB

Signed-off-by: John Wang <wangzhiqiang.bj@bytedance.com>
Link: https://lore.kernel.org/r/20200929063955.1206-1-wangzhiqiang.bj@bytedance.com


Signed-off-by: Joel Stanley <joel@jms.id.au>