This patch fixes an issue in the implementation of DUP/CPY where certain
immediates were not accepted. Immediates should be interpreted as a two's
complement encoding of a value that fits the number of bits of the element
type.
mov z0.b, p0/z, #127
<=> mov z0.b, p0/z, #-129
<=> mov z0.b, p0/z, #0xffffffffffffff7f
This behaviour is in line with the GNU assembler.
Reviewed By: c-rhodes
Differential Revision: https://reviews.llvm.org/D94776
