defconfig: Enable sdx external ipc driver for sdxprairie

This driver will enable communication between sdx and external
application processor. Sdx and external AP communicate with
each other using gpios.

Change-Id: Ibb2c6dfec52722f6a7147f4544e9c4c46e4d3abd
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>