What is OTP for selecting GPIO function in PMICs?
They're not referring to CMOS or NMOS, the options are CMOS or N-Channel open-drain.
The CMOS option can push or pull the pin up or down, while the open-drain option can only pull the pin down (relying on an external pull-up resistor).  

OTP is almost certainly referring to One-Time-Programming.
There doesn't seem to be any indication in that document on how this programming is done though.