acpi_ec: request for review and testing

[Andriy Gapon]

Here's a patch for acpi_ec that is developed in cooperation with David Naylor who
also did all the testing:
http://people.freebsd.org/~avg/acpi_ec.2.patch

The patch quite aggressively changes a few things and tries to make logic more
robust with respect to EC behavior.

I ask everybody, who is able to help, to test the patch, please.
I am interested in all kinds of reports.
If your EC "misbehaves", then there is a chance that the patch will fix that.
If your EC works fine, then make sure that I don't break it with the patch.

Short description of the changes:
- attempt to retry some commands for which it is possible (read, query)
- always make a short sleep before checking EC status in polled mode
- periodically poll EC status in interrupt mode
- change logic for detecting broken interrupt delivery and falling back to polled mode
- check that EC is ready for input before starting a new command, wait if necessary

Big thanks in advance.
-- 
Andriy Gapon