ti_config_fragments: v8_rpmsg: Enable rpmsg-proto module

Add support to build the rpmsg sockets driver "rpmsg-proto"
explicitly for K3 SoCs. This enables the TI MessageQ IPC stack
to be used with the MCU R5F remote processors _only_ on AM65x
SoCs using firmwares from the IPC 3.x project. There is no
RTOS support for the MessageQ stack on J721E SoCs.

Signed-off-by: Suman Anna <s-anna@ti.com>