ARM: dts: msm: Add npu mailbox controller 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: I998c66c55ce0d959a3fe0dc382d2bbb9ccbe8e84
Signed-off-by: Da Hoon Pyun <dpyun@codeaurora.org>