[AArch64][AdvSIMDScalar] Update the kill flags correctly.

We used to simply set the kill flags to true when transforming a scalar
instruction to a vector one.
SrcScalar1 = copy SrcVector1
... = opScalar SrcScalar1
=>
SrcScalar1 = copy SrcVector1
... = opVector SrcVector1<kill>

This is obviously wrong. The proper update consists in:
1. Propagate the kill status from the copy to the new opVector
2. Reset the kill status on the copy, since the live-range of
   SrcVector1 got extended.

This fixes some of the machine verifier errors for AArch64 with make check.

llvm-svn: 267180