Update the encodings to add the new ops

- Reflected the changes we did on the spec on the encodings (readm -> read_u8, read_s8, read_16, writem -> write_8 & write_16, added sar).
- Shuffled around the opcodes a bit so they are in a nicer order
- Extened wait to have a 4 bit imm field (so we can select what to wait on)