msm: ADSPRPC: Support SMD communication for legacy chipsets

Add new probe function to parse device nodes of legacy chipsets
and driver changes to support SMD communication.
Modify the documentation of legacy device nodes and add sub
node properties.

Change-Id: Ic3e111e36fb9a44fb223d62b0e7df68d7fd3ed7e
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>