Add two sysfs node: core_id, config_id, user can read them to fetch the
HW product information.

Also, use memset to initialize config_id, rather than quirky C syntax.
Courtesy of Nathan Chancellor <natechancellor@gmail.com>.
Signed-off-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
[Merged Nathan's patch that uses memset to initialize config_id into
original patch as the fixes tag changed due to rebase, reworded the
commit to reference the merged patch]
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>