ARM: dts: msm: Add SMP buffer reservation limit on msm8226

Add an optional property to restrict maximum SMP block allocation
required for targets like 8x26, where total available SMP blocks
are limited.

Change-Id: I08827f16ae673a1b9884c844dc169e13b9d406ab
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>