Introduce aarch64_insn_gen_{nop|branch_imm}() helper functions, which
will be used to implement jump label on ARM64.
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NJiang Liu <liuj97@gmail.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>