Driver Core: Rework platform suspend/resume, print warning

This patch reworks the platform driver code for legacy
suspend and resume to avoid installing callbacks in
struct device_driver. A warning is also added telling
users to update the platform driver to use dev_pm_ops.

The functions platform_legacy_suspend()/resume() directly
call suspend and resume callbacks in struct platform_driver
instead of wrapping things in platform_drv_suspend()/resume().

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>