edgetpu: prevent system suspend when clients are active

Implement minimal suspend/resume handlers to notify the system the
device cannot go to sleep state when a client is holding the firmware
wakelock.

Bug: 181578920

Signed-off-by: Erick Reyes <erickreyes@google.com>
Change-Id: I387d073c9b2a9012b84427805918d3731171e7e0
(cherry picked from commit 6438b8f6536c9383ae0e59e4a0b22de7e7063afb)