CPU Schedulers Offline
What you see makes perfect sense given the information available.

SQL Server 2012 Standard Edition is limited to the lesser of 4 sockets or 16 physical cores.

Since you have 40 cores (likely 2 socket 10 core + HT) 16 physical cores is going to be 32 logical cores (because of HT). If you have 40 total, I would EXPECT 8 to be VISIBLE OFFLINE due to licensing.

Features Supported by the Editions of SQL Server 2012 - Cross-Box Scale Limits

Edit: Additional Information

Depending on the OS involved the schedules may be bound to CPUs that are also making an unbalanced NUMA memory configuration for your system. While it is highly unlikely that this will cause you any issues (since it wasn't noticed that all the CPUs were being used in the first place) it could have a much higher impact on a highly used system where the foreign memory access can really add up.