target-ppc/machine.c: Drop unnecessary ifdefs

machine.c is only compiled for softmmu targets, so checks for
!defined(CONFIG_USER_ONLY) are unnecessary and can be dropped.

Signed-off-by: Juan Quintela <quintela@redhat.com>
[AF: Use more verbose commit message suggested by PMM]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>
