Add vaaddu/vasubu; change vaadd/vasub opcodes
Add vaaddu/vasubu; change vaadd/vasub opcodes

See https://github.com/riscv/riscv-v-spec/commit/c2f3157e34d3a0f77ccbbc502bdf1530da17aba8

riscv/riscv-opcodes,riscv/riscv-opcodes