pan/bi: Add HADD.v4s8.rhadd packing test cases

To confirm the XML is right.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18656>

src/panfrost/bifrost/valhall/test/assembler-cases.txt

@@ -239,3 +239,4 @@ c4 c0 40 10 71 c0 b6 00    LSHIFT_AND.v4i8 r0, 0x1000000.b3333, 0x0.b00, ^r0
 40 00 13 00 80 c0 90 00    V2U8_TO_V2F16 r0, ^r0.b02
 41 40 00 40 00 c0 aa 00    IADD.v4s8.saturate r0, ^r1, ^r0
 41 40 01 40 00 c0 aa 00    ISUB.v4s8.saturate r0, ^r1, ^r0
+41 40 0b 40 00 c0 aa 00    HADD.v4s8.rhadd r0, ^r1, ^r0

src/panfrost/bifrost/valhall/test/test-packing.cpp

@@ -320,3 +320,9 @@ TEST_F(ValhallPacking, LdTileV3F16) {
                          BI_REGISTER_FORMAT_F16, BI_VECSIZE_V3),
         0x0078840423033c40);
 }
+
+TEST_F(ValhallPacking, Rhadd8) {
+   CASE(bi_hadd_v4s8_to(b, bi_register(0), bi_discard(bi_register(1)),
+                        bi_discard(bi_register(0)), BI_ROUND_RTP),
+        0x00aac000400b4041);
+}