drm/radeon/r600_cs: remove r600_cs_legacy_get_tiling_conf() declaration

r600_cs_legacy_get_tiling_conf() has been removed since
commit 8333f607 ("drm/radeon: remove UMS support"),
so remove it.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220913024847.552254-3-cuigaosheng1@huawei.com