dt-bindings: mhi: add wake capable channel property

Add an optional channel property to identify time critical
transfer channels. MHI host uses this property to abort
system suspend to process incoming data.

CRs-Fixed: 2348867
Change-Id: I613f55b793ab0c75d276eb06b26ccf7c70f9c619
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>