drm/amd/display: Add missing "Copy GSL groups when committing a new context"

[Why]
"Copy GSL groups when committing a new context" patch was accidentally
removed during a refactor

Patch: 21ffcc94 ("drm/amd/display: Copy GSL groups when committing a new context")

[How]
Re add it

Fixes: b6e881c9 ("drm/amd/display: update navi to use new surface programming behaviour")
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>