nir: Fix read depth for predecessors
In some non-trivial cases (the amber script file in the merge request description) phi instruction has more than 32 elements in predecessors tree and that isn't recursion, just large tree. In that case, phis not fully converted into a register or mov, but successfully removed.
The fix removes the counter and adds container of visited blocks.
Closes: #3690 (closed)
Cc: mesa-stable
Signed-off-by: Mykhailo Skorokhodov mykhailo.skorokhodov@globallogic.com