drm/i915: Add GuC ukernel logging related fields to fw interface file

The first page of the GuC log buffer contains state info or meta data
which is required to parse the logs contained in the subsequent pages.
The structure representing the state info is added to interface file
as Driver would need to handle log buffer flush interrupts from GuC.
Added an enum for the different message/event types that can be send
by the GuC ukernel to Host.
Also added 2 new Host to GuC action types to inform GuC when Host has
flushed the log buffer and forcefuly cause the GuC to send a new
log buffer flush interrupt.

v2:
- Make documentation of log buffer state structure more elaborate &
  rename LOGBUFFERFLUSH action to LOG_BUFFER_FLUSH for consistency.(Tvrtko)

v3: Add GuC log buffer layout diagram for more clarity.

Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Signed-off-by: Akash Goel <akash.goel@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>