[POWERPC] 4xx: Introduce cpu_setup functionality to 44x platform

This adds cpu_setup functionality for ppc44x platform.
Low level cpu-spefic initialization routines should be
placed in cpu_setup_44x.S and a callback should be
added to cputable. The cpu_setup is invoked
by identify_cpu() function at early init.

Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>