ena: Add support for reset request over AENQ

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 (mentor)
MFC after: 2 weeks
Sponsored by: Amazon, Inc.