board_f: Add a mach_cpu_init callback

board_f: Add a mach_cpu_init callback

Currently we have a mismash of architectures which use arch_cpu_init
from architecture-wide code (arc, avr32, blackfin, mips, nios2, xtensa)
and architectures which use arch_cpu_init from machine/SoC level code
(arm, x86).

In order to clean this mess up & allow for both use cases, introduce a
new mach_cpu_init callback which is run immediately after arch_cpu_init.
This will allow for architectures to have arch-wide code without needing
individual machines to all implement their own arch_cpu_init with a call
to some common function.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Simon Glass <sjg@chromium.org>