i2c: enable async suspend/resume for i2c adapters

Enable async suspend/resume of i2c adapters. It enormously helps with
reducing the resume time of systems (as much as 20%-40%) where I2C devices
can take significant time (100s of ms) to resume.

Signed-off-by: Rajat Jain <rajatja@google.com>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>