defconfig: 8084: Enable ADSP RPC driver

The ADSP RPC driver allows for clients to make remote method
invocations across processor boundary to DSP processor. Enable
this driver for APQ8084.

Change-Id: I6407763ffa1962d69f45cd10715dfbf7d0a22873
Acked-by: Sathish Ambley <sambley@qti.qualcomm.com>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>