This commit fixes three issues in MESI_Three_Level and MESI_Two_Level
implementations (MEI_Three_Level_HTM might still have issues).
1) Define functional read priorities for the cache controllers which
have states with Maybe_Stale access permission (L1 > L2 > Directory).
2) Fix incorrect access permissions in MESI_Three_Level-L1cache:
* S_IL0 is Read_Only, it is waiting for L0 to acknowledge the
invalidation request before moving to SS, also a Read_Only state.
* E_IL0 is Maybe_Stale, its contents might be valid, since there is a
transition (E_IL0, L0_Ack, EE) with no writeback data.
* M_IL0 is Maybe_Stale, its contents might be valid, since there is a
transition (M_IL0, L0_Ack, MM) with no writeback data.
3) Add missing message types carrying valid data in functional reads:
* INV_DATA is a writeback from L0 to L1.
* DATA is a response to GET_S, but there are scenarios where it might
be the only place with valid data (e.g. during L2 replacement).
Change-Id: Ie44fa317027f9ede272967e7461d337e14355eec
c31bc284a8