This patch adds the appropriate macros, tests and codec entries to encode the following variants:
PRFB <prfop>, <Pg>, [<Xn|SP>{, #<imm>, MUL VL}]
PRFD <prfop>, <Pg>, [<Xn|SP>{, #<imm>, MUL VL}]
PRFH <prfop>, <Pg>, [<Xn|SP>{, #<imm>, MUL VL}]
PRFW <prfop>, <Pg>, [<Xn|SP>{, #<imm>, MUL VL}]
Issue: #3044