[POWERPC] Move CPM command handling into the cpm drivers

This patch moves the CPM command handling into commproc.c
for CPM1 and cpm2_common.c. This is yet another preparation
to get rid of drivers accessing the CPM via the global cpmp.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Acked-by: Scott Wood <scottwood@freescale.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vitaly Bordug <vitb@kernel.crashing.org>