Fix a couple of bugs in the ITS support code:

Fix a couple of bugs in the ITS support code:

- Don't dereference sc_prop if we're not handling an LPI.  Fixes a crash
  on qemu when emulating a GICv3 without ITS (and therefore no LPIs(.

- Use the true IPL when calculating the priority of an LPI.  The old
  code used a variable that still had the IPL_MPSAFE flag in it.

- Write to the right GITS_BASERn instead of ialways writing to GITS_BASER0.

- Flush the cache after initializing/modifying the in-memory tables.  The
  GICv3 on the SynQuacer isn't fully coherent and only supports the
  "non-shareable" attribute for its in-memory tables.  So we have to flush
  the cache to the point of coherency to guarentee that the GIC sees our
  changes to those tables.  Throw in a full memory barrier for good measure.

Also add support for the SynQuacer pre-ITS.

ok jsg@, patrick@