ena: Add support for reset request over AENQ

[osamaabb_amazon.com]

Summary

In order to support reset request message from the device to the driver,
over AENQ, which in turn should cause the driver to trigger reset, the
following was added:

1. New AENQ group - ENA_ADMIN_DEVICE_REQUEST_RESET, to support the new message from the device sent via the AENQ to the driver.
2. New reset reason - ENA_REGS_RESET_DEVICE_REQUEST, which is used in order to indicate that the reset was triggered by the driver following the device request.

Approved by: cperciva
MFC after: 2 weeks
Sponsored by: Amazon, Inc.