powerpc/8xxx: Distinguish between incompatible SEC h/w types

CONFIG_SYS_FSL_SEC_COMPAT is set to 2 for the SEC 2.x and SEC 3.x.
Parts with newer SEC h/w versions will increment the number to
accomodate incompatible code changes.

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