ucm2: rk3399-gru-sound: Add missing symlink from conf.d tree

ucm2: rk3399-gru-sound: Add missing symlink from conf.d tree

Commit b0f6cdf68d8f ("ucm.conf: turn off support for V2Module and V2Name
by default") disabled looking up UCM configs via the kernel module
symlinks. The rk3399-gru-sound card doesn't have a conf.d symlink yet,
add one so that boards using it can find its UCM config again.

Fixes: https://github.com/alsa-project/alsa-ucm-conf/pull/162
Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>