ppc: Unlock cache-as-ram in a consistent manner

ppc: Unlock cache-as-ram in a consistent manner

Previously, non-e500 architectures only unlocked their data cache which
was used as early RAM when booting to Linux using the "bootm" command.
This change causes all PPC boards with CONFIG_SYS_INIT_RAM_LOCK defined
to unlock their data cache during U-Boot's initialization.  This
improves U-Boot performance and provides a common cache state when
booting to different OSes.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>