drivers/perf: hisi: Add identifier sysfs file

To allow userspace to identify the specific implementation of the device,
add an "identifier" sysfs file.

Encoding is as follows (same for all uncore drivers):
hi1620: 0x0
hi1630: 0x30

Signed-off-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/1602149181-237415-2-git-send-email-john.garry@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>