powerpc: Remove unused MPC8540/60ADS code

Remove some code, primarily CPM2 related, that is now unused since the
removal of MPC8540/60ADS.

Fixes 3913191c ("powerpc: mpc8540ads: mpc8560ads: Drop support for MPC8540/60ADS")
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>