powerpc 83xx/85xx: Merge lbc upmconfig code

Each platform had its own version of the upmconfig, despite the
init process being identical.  Now that we have a spot for common
lbc code, create a common upmconfig() there.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>