Patmos: fix type equivalance check

* check for NULL, e.g., when the function target is unknown
patmos: fix delay slot filler

* handle empty successor blocks
patmos: fix splitting of basic blocks

* account for first instruction after splitting a block
patmos: improved stack cache "analysis"

* propagate max. stack cache usage from loads/stores to ensure
* downsize ensures depending on actual stack cache usage
* propagate max. stack cache usage of call sites accross basic blocks
* run stack cache analysis before delay slot filler and function splitter