ARM: dts: msm: Add kraitbw-l2pm device for 8974

This device provides the hardware details needed by the kraitbw_l2pm
devfreq governor to measure the DDR usage from the Krait CPU subsystem and
the IRQ that's needed to react quickly to usage changes.

Change-Id: I778a36839c9b2279ab2d912715cd7eba091fe25f
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>