Update syntax instructions vmv, vmerge, vfmv and vfmerge

Recently the V-extension updated the syntax and meaning of these
instructions.

Because the new syntax overlaps with the new syntax of `vadc` and `vsbc` I have
also updated them. See #9.

Remove the innecessary intrinsic llvm.int.epi.broadcast_mask which is
now entirely covered by llvm.int.epi.vmerge.

Remove the innecessary clang builtin __builtin_epi_vbroadcast_*_mask
because now __builtin_epi_vmerge_* does the same.