board_f: Use static print_cpuinfo if CONFIG_CPU is active

When the DM CPU drivers are active, printing information about a CPU
should be delegated to a matching driver.

Hence, add a static print_cpuinfo that implements this delegation when
DM CPU drivers are active.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mario Six <mario.six@gdsys.cc>
Changed condition to CONFIG_IS_ENABLED(CPU):
Signed-off-by: Simon Glass <sjg@chromium.org>