arm64: armv8_deprecated: Fix warning in isndep cpuhp starting process

The function run_all_insn_set_hw_mode() is registered as startup callback
of 'CPUHP_AP_ARM64_ISNDEP_STARTING', it invokes set_hw_mode() methods of
all emulated instructions.

As the STARTING callbacks are not expected to fail, if one of the
set_hw_mode() fails, e.g. due to el0 mixed-endian is not supported for
'setend', it will report a warning:

```
CPU[2] cannot support the emulation of setend
CPU 2 UP state arm64/isndep:starting (136) failed (-22)
CPU2: Booted secondary processor 0x0000000002 [0x414fd0c1]
```

To fix it, add a check for INSN_UNAVAILABLE status and skip the process.

Signed-off-by: Wei Li <liwei391@huawei.com>
Tested-by: Huisong Li <lihuisong@huawei.com>
Link: https://lore.kernel.org/r/20240423093501.3460764-1-liwei391@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>