PM / Runtime: Add sysfs debug files

Add a few sysfs files relating to runtime power management for
advanced debug purposes:

runtime_enabled: is runtime PM enabled for this device? States
	are "enabled", "disabled", "forbidden" or a combination
	of the latter two.

runtime_status:	what state is the device in currently? E.g., it
	reports "suspended" for runtime-suspended devices, and
        "active" for active devices. NOTE: if runtime_enabled
	returns "disabled", the value of this file may not
	reflect its physical state.

runtime_usage: the runtime PM usage count of a device

runtime_active_kids: the runtime PM children usage count of a device, or
	0 if the ignore_children flag is set.

Also, CONFIG_PM_SLEEP_ADVANCED_DEBUG is not defined in any Kconfig
file, so replace it with CONFIG_PM_ADVANCED_DEBUG.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>