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>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c

@@ -1642,6 +1642,17 @@ void dcn20_program_front_end_for_ctx(
 	struct dce_hwseq *hws = dc->hwseq;
 	DC_LOGGER_INIT(dc->ctx->logger);
 
+	/* Carry over GSL groups in case the context is changing. */
+       for (i = 0; i < dc->res_pool->pipe_count; i++) {
+               struct pipe_ctx *pipe_ctx = &context->res_ctx.pipe_ctx[i];
+               struct pipe_ctx *old_pipe_ctx =
+                       &dc->current_state->res_ctx.pipe_ctx[i];
+
+               if (pipe_ctx->stream == old_pipe_ctx->stream)
+                       pipe_ctx->stream_res.gsl_group =
+                               old_pipe_ctx->stream_res.gsl_group;
+       }
+
 	if (dc->hwss.program_triplebuffer != NULL && dc->debug.enable_tri_buf) {
 		for (i = 0; i < dc->res_pool->pipe_count; i++) {
 			struct pipe_ctx *pipe_ctx = &context->res_ctx.pipe_ctx[i];