drivers: i2c: support per-device async suspend

Adds support for opting-in to async suspend on a per-device basis
through client flags and device tree.

Bug: 134704142
Test: Build and Run
Change-Id: I5609700cbff5c961dc820a9bcf9a4d57eafcd3b2
Signed-off-by: Harpreet "Eli" Sangha <eliptus@google.com>