adsprpc: Enable fastrpc driver

Add fastrpc driver files, which provide a communication
mechanism that allows for clients to make remote method
invocations across processor boundary to applications
DSP processor.

Change-Id: Ifd82dfd390634a8b57201aa255d9753818452188
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>