Making sl coalescing logic a little clearer, preventing coalescing in the case where the sl has a non-contiguous KVA but the physical pages happen to be adjacent.

Style fixes. Initialize sl outside the mapping loop, since it is incremented inside the loop.

• Fix logic errors around call to sync_buf and bounce buffer cache maintenance
• Remove sync_buf call for unmapped case: cache operations in pmap_quick_enter_page()->pmap_kenter()->pmap_fix_cache() make sync_buf irrelevant

• Simplify loop in sync_sl

Adding assert on non-contiguous pages

Port unmapped bounce buffer alignment fix from x86

Narrow the scope of the temporary bounce buffer mappings