ARM: dts: msm: Add node for mpm sleep counter for sdxpoorwills

Add device node for mpm 2 sleep counter which is required
for the boot stats KPI reporting on sdxpoorwills target.

Change-Id: Idb5b747de27f189e967f2c6ba8b2f65176abe5b4
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>