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

The perf tool can match the Yitian 710 DDR metric through the identifier.
Signed-off-by: Jing Zhang <renyu.zj@linux.alibaba.com>
Acked-by: Ian Rogers <irogers@google.com>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Link: https://lore.kernel.org/r/1687245156-61215-2-git-send-email-renyu.zj@linux.alibaba.comSigned-off-by: Will Deacon <will@kernel.org>