LynxPoint: Move RCBA helper function to its own file

So it can get used in both romstage and ramstage.

Change-Id: Ief9eaafdd91df2a7b668de1a9b83aea3af3ff894
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/2802
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
4 files changed