[POWERPC] adb: Replace sleep notifier with platform driver suspend/resume hooks

This replaces the pmu sleep notifier that adb had with suspend/resume
hooks in a new platform driver/device.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>