ti_config_fragments: rpmsg: Enable rpmsg-proto module

Add support to build the rpmsg sockets driver "rpmsg-proto"
explicitly now for both v5 and v7 platforms. The dependent
REMOTEPROC is already enabled as built-in in the needed
defconfigs (multi_v7_defconfig and davinci_all_defconfig).
The other dependent RPMSG_VIRTIO module is also enabled
explicitly.

These options enable the TI MessageQ IPC stack for various
v5 (OMAP-L138) and v7 (66AK2x, DRA7xx, AM57xx etc) platforms.

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