[wasm-simd][liftoff][arm][arm64] Implement rounding average unsigned

Bug: v8:9909
Change-Id: I9145ac93392073f01e2df9fec8eeae0b6e75dd00
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2145238
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67132}

src/wasm/baseline/arm/liftoff-assembler-arm.h

@@ -2106,13 +2106,15 @@ void LiftoffAssembler::emit_i8x16_max_u(LiftoffRegister dst,
 void LiftoffAssembler::emit_i8x16_rounding_average_u(LiftoffRegister dst,
                                                      LiftoffRegister lhs,
                                                      LiftoffRegister rhs) {
-  bailout(kSimd, "i8x16_rounding_average_u");
+  vrhadd(NeonU8, liftoff::GetSimd128Register(dst),
+         liftoff::GetSimd128Register(lhs), liftoff::GetSimd128Register(rhs));
 }
 
 void LiftoffAssembler::emit_i16x8_rounding_average_u(LiftoffRegister dst,
                                                      LiftoffRegister lhs,
                                                      LiftoffRegister rhs) {
-  bailout(kSimd, "i16x8_rounding_average_u");
+  vrhadd(NeonU16, liftoff::GetSimd128Register(dst),
+         liftoff::GetSimd128Register(lhs), liftoff::GetSimd128Register(rhs));
 }
 
 void LiftoffAssembler::emit_i8x16_abs(LiftoffRegister dst,

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -1491,13 +1491,13 @@ void LiftoffAssembler::emit_i8x16_max_u(LiftoffRegister dst,
 void LiftoffAssembler::emit_i8x16_rounding_average_u(LiftoffRegister dst,
                                                      LiftoffRegister lhs,
                                                      LiftoffRegister rhs) {
-  bailout(kSimd, "i8x16_rounding_average_u");
+  Urhadd(dst.fp().V16B(), lhs.fp().V16B(), rhs.fp().V16B());
 }
 
 void LiftoffAssembler::emit_i16x8_rounding_average_u(LiftoffRegister dst,
                                                      LiftoffRegister lhs,
                                                      LiftoffRegister rhs) {
-  bailout(kSimd, "i16x8_rounding_average_u");
+  Urhadd(dst.fp().V8H(), lhs.fp().V8H(), rhs.fp().V8H());
 }
 
 void LiftoffAssembler::emit_i8x16_abs(LiftoffRegister dst,