ARM: dts: msm: Update MHI device properties for SDX20

Modem Host Interface (MHI) is used by clients to
communicate between device and host. Software and
hardware channels communicate over IPA DMA. Update
MHI device properties for SDX20.

Change-Id: Id8f9ca99b2b9dc835907dfbd4b6febaeef1bdbe6
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>