ARM: dts: msm: Enable smp2p mailbox for atoll

The mailbox controller implemented in NPU works as a bridge
between ipcc_mproc mailbox controller and its clients. It is
required because npu driver needs to control when IPCC irq can
be sent to NPUQ6.

Change-Id: I3b9d0eb77c834c10ddeed6aa2fea3858cdb6745e
Signed-off-by: Da Hoon Pyun <dpyun@codeaurora.org>