soc: qcom: msm_rtb: Add support for hotplug RTB logging

Hotplug events are particularly interesting from system
point of view and tracing around the hotplug events would
provide essential information that could be used to debug
system issues.

Currently the code exists for arm32 only. Move it into its
own file so that it can be used for arm64 as well.

Change-Id: I695aeabe8742de3599b83dbf646d6c6be627057e
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>
Signed-off-by: David Keitel <dkeitel@codeaurora.org>