Fix #115 - xperm.b / xperm.n /rev.b mnemonics

Renaming:
xperm.b -> xperm8
xperm.n -> xperm4
rev.b   -> brev8

 Changes to be committed:
	modified:   riscv-crypto-scalar-zbkb.adoc
	modified:   riscv-crypto-scalar-zbkx.adoc
	modified:   riscv-crypto-spec-scalar.adoc
	modified:   ../../extern/riscv-bitmanip