etnaviv: rs: Support 8bpp for clears

Needs a GPU with S8 support.

Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37014>

src/gallium/drivers/etnaviv/etnaviv_rs.c

@@ -284,6 +284,10 @@ etna_rs_gen_clear_cmd(struct etna_context *ctx,
    uint32_t format;
 
    switch (util_format_get_blocksizebits(psurf->format)) {
+   case 8:
+      assert(VIV_FEATURE(screen, ETNA_FEATURE_S8));
+      format = RS_FORMAT_S8;
+      break;
    case 16:
       format = RS_FORMAT_A4R4G4B4;
       break;