In the E500CORERM, there is time base registers (two 32 bits counters), and some Decrementer registers.
In the P2020RM, I see only the eight decrementer registers.
The time base register is not available in the P2020 ?
Edit: I found sheet 156 of P2020RM the timebase, but it's a little poor documented.
P2020 contains E500 cores, and thus it contains everything that the E500 document describes, regardless of whether it's repeated in the P2020RM. The timers you found in P2020RM are completely separate from the core timebase/decrementer, and are not attached to any particular core.