[VPlan] Allow VPInstruction::PtrAdd as a user of EVL (#175506)
Fixes #175058
Similar to #175028, on RV64 we insert a zext in between most uses of EVL
so most of the VPlanVerifier EVL checks don't fire unless we're
compiling for RV32.
In this case, we're experiencing a crash because we can have a PtrAdd
that uses EVL. This fixes it by adding PtrAdd to the list of allowed
instructions