PM / Sleep: Require CAP_BLOCK_SUSPEND to use wake_lock/wake_unlock

commit 11388c87 upstream.

Require processes wanting to use the wake_lock/wake_unlock sysfs
files to have the CAP_BLOCK_SUSPEND capability, which also is
required for the eventpoll EPOLLWAKEUP flag to be effective, so that
all interfaces related to blocking autosleep depend on the same
capability.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Michael Kerrisk <mtk.man-pages@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>