drivers: llcc: Create child platform device for llcc_perfmon

llcc_perfmon driver can reuse register mappings from llcc driver,
hence creates child nod device qcom_lcc_perfmon.

Change-Id: Ic444b22faf2776e297b9c4c30051d69130d0a349
Signed-off-by: Avinash Philip <avinashp@codeaurora.org>
[rananta@codeaurora.org: Resolved trivial merge conflicts]
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>