drm/amd/display: Fix multiple memory leaks reported by coverity

coccinelle patch used:

@@ expression enc1,vpg,afmt; @@
-       if (!enc1 || !vpg || !afmt)
+       if (!enc1 || !vpg || !afmt) {
+               kfree(enc1);
+               kfree(vpg);
+               kfree(afmt);
                return NULL;
+       }

Addresses-Coverity-ID: 1466017: ("Resource leaks")

Reviewed-by: Aurabindo Jayamohanan Pillai <Aurabindo.Pillai@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>