rvsol: RISCV.sol Compatibility with MIPS.sol

[pcw109550]

Description

op-challenger on the monorepo wraps around the FPVM contract using hardcorded ABI generated for MIPS.sol. It calls oracle method to access public preimageoracle address embedded in the contract.

To make this compatible, I have changed the name of variable which stores the preimage oracle address at RISCV.sol to oracle as well.

Another approach can be, making op-challenger more configurable, taking ABI as a argument, but I thought changing the VM contract is easier.

Updated contract bindings.

Current MIPS binding metadata:

{"type":"function","name":"oracle","inputs":[],"outputs":[{"name":"oracle_","type":"address","internalType":"contractIPreimageOracle"}],"stateMutability":"view"}

Updated RISCV binding metadata:

{"type":"function","name":"oracle","inputs":[],"outputs":[{"name":"","type":"address","internalType":"contractIPreimageOracle"}],"stateMutability":"view"}