firmware: use power efficient workqueue for unloading and aborting fw load

Allow the scheduler to select the most appropriate CPU for running the
firmware load timeout routine and delayed routine for firmware unload.
This extends idle residency times and conserves power.

This functionality is enabled when CONFIG_WQ_POWER_EFFICIENT is selected.

Cc: Ming Lei <ming.lei@canonical.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Shaibal Dutta <shaibal.dutta@broadcom.com>
[zoran.markovic@linaro.org: Rebased to latest kernel, added commit message.
Fixed code alignment.]
Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>