ARM: dts: msm: add support for bandwidth scaling event ring

Add a dedicated low priority SW event ring for bandwidth
scaling feature.

CRs-Fixed: 2479785
Change-Id: I656458433b81eaad8e610f04117e0d929fbc1c40
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>