The nCEO pin can be used as I/O. However, depending on the Quartus II version, the Default setting is
It is set to "Use as Programming Pin", so you need to set this setting to "Use as regular I/O".

Set the I/O using the method below, compile again, and check if placement is possible.
・ Select Assignments ⇒ Device ⇒ Device and PinOptions from the Quartus II TOP screen.
・ Select the Dual-Purpose Pin item
・ Change the Value column of nCEO to Use as regular I/O and OK.

* There are device families (eg Stratix III, Stratix IV, etc.) where the nCEO pin is a dedicated pin.
In that case, please note that there is no above setting item.