Driver core: move platform device creation helpers to .init.text (if MODULE=n)

Platform devices should only be called by init code, so it should be
possible to move creation helpers to .init.text -- at least if modules
are disabled.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>