thermosphere: use barriers and caches *properly*. Cache code refactoring

- set/way cache ops create losses of coherency, do not broadcast and are only meant to be used on boot, period.

Cache ops by VA are **the only way** to do data cache maintenance.

Fix a bug where the L2 cache was evicted by each core. It shouldn't have.

- Cleaning dcache to PoU and invalidating icache to PoU, by VA is sufficient for self-modifying code

- Since we operate within a single cluster and don't do DMA, we almost always operate within the inner shareability domain

(commit untested on real hw)

thermosphere/src/start.s

@@ -50,8 +50,11 @@ _startCommon:
     dsb     sy
     isb
 
-    mov     x2, x0
+    bl      cacheClearLocalDataCacheOnBoot
+    cbz     x19, 1f
+    bl      cacheClearSharedDataCachesOnBoot
 
+1:
     // Get core ID
     // Ensure Aff0 is 4-1 at most (4 cores), and that Aff1, 2 and 3 are 0 (1 cluster only)
     mrs     x0, mpidr_el1