[wasm] Skip wasm simd tests for big endian.

Tests cctest/test-run-wasm-simd/RunWasm_I16x8ConvertI32x4_turbofan
and cctest/test-run-wasm-simd/RunWasm_I8x16ConvertI16x8_simd_lowered
will be skipped for big endian until implementation for big endian is
done correctly.

Change-Id: Ia6253070ede207f437e4b710a656bce8d65e412e
Reviewed-on: https://chromium-review.googlesource.com/1113307
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Aseem Garg <aseemgarg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54176}

test/cctest/cctest.status

@@ -451,8 +451,10 @@
   'test-run-wasm-simd/RunWasm_S8x16Irregular_interpreter': [SKIP],
   'test-run-wasm-simd/RunWasm_S8x16Blend_interpreter': [SKIP],
   'test-run-wasm-simd/RunWasm_S8x16Concat_interpreter': [SKIP],
+  'test-run-wasm-simd/RunWasm_I16x8ConvertI32x4*': [SKIP],
+  'test-run-wasm-simd/RunWasm_I8x16ConvertI16x8*': [SKIP],
 
-}],  # 'arch == mips or arch == mips64'
+}],  # 'byteorder == big'
 
 ##############################################################################
 ['variant == stress_incremental_marking', {