[AArch64] Avoid materializing constant 1 when generating cneg instructions.

Instead of

 cmp w0, #1
 orr w8, wzr, #0x1
 cneg w0, w8, ne

we now generate

 cmp w0, #1
 csinv w0, w0, wzr, eq

PR28965

llvm-svn: 285217