Introduce wakelock_use()

Introduce wakelock_use(). This macro declares that a domain uses
wakelocks.

Wakelocks require both read-write access to files in /sys/power, and
CAP_BLOCK_SUSPEND. This macro helps ensure that both capabilities and
file access are granted at the same time.

Still TODO: fix device specific wakelock use.

Change-Id: Ib98ff374a73f89e403acd9f5e024988f59f08115