ARM: dts: msm: share slpi context bank for fastrpc in sm8150

Add a property to one slpi context bank to control how many
fastrpc sessions can share the same context bank.

Change-Id: Ie36da30b9a374c9eadd43d1c7d2d9429170b1721
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>