Solution:
Yes, Any GBIN pin can be used to drive the reference clock input to the PLL on iCE40.
If the PLL instantiated, the the GPLL_IN dual mode cannot be used as input to other pins but could only be used as output pin.
With this GPLL_IN pin, is preferably used as input for the PLL reference clock input.
If this is not possible, it is also valid to use any other GBIN input for the PLL reference clock.