AArch64 defines new registers for the feature step2 (Enhanced Software Step
Extension). step2 is an Armv9.5-A feature.

This patch also adds relevant tests. Regression tested on aarch64-none-elf,
and no regression found.
---
 .../aarch64/sysreg/armv9_5-a-sysregs-archv9_4-unsupported.l   | 4 ++++
 gas/testsuite/gas/aarch64/sysreg/armv9_5-a-sysregs.d          | 2 ++
 gas/testsuite/gas/aarch64/sysreg/armv9_5-a-sysregs.s          | 3 +++
 include/opcode/aarch64.h                                      | 3 +++
 opcodes/aarch64-sys-regs.def                                  | 1 +
 5 files changed, 13 insertions(+)