Disable constant folding of [Gpu]Alloc in more case.

Since we do constant folding earlier, this make a GpuAlloc test fail.
This could also speed some code as this allow more op to work inplace.
Remove condition that is always True as we check if it was "output" before and it is the only string supported.
Fix test as now more gemv are inplace.
Merge pull request #1782 from nouiz/alloc_cst_fold

Alloc cst fold