km/ppc: remove km-mpc8360.h and km-mpc832x.h

Next step to get rid of the header files in icnlude/configs. Move
most of the defines to km83xx.c directly. Some remaining defines
which should go to Kconfig are moved to km-mpc83xx.h for now.

Also remove some unused defines and move one define to powerpc.env
as we only need it there.

Signed-off-by: Holger Brunck <holger.brunck@hitachienergy.com>