turnip: sysmem vs GMEM decision
We currently use the GMEM path whenever possible, unless TU_DEBUG=sysmem
is set, but this performs sub-optimally in many cases.
Some factors which can make it a good idea to use sysmem:
- Few draws
-
LOAD_OP_LOAD
/STORE_OP_STORE
attachments (these are a NOP for sysmem path) - No depth attachment