Improve naive SkColorXform to half floats

src/opts/SkNx_neon.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkNx_neon_DEFINED
 #define SkNx_neon_DEFINED
 
@@ skipping 465 matching lines @@
 }
 
 template<> inline Sk4h SkNx_cast<uint16_t, int>(const Sk4i& src) {
     return vmovn_u32(vreinterpretq_u32_s32(src.fVec));
 }
 
 static inline Sk4i Sk4f_round(const Sk4f& x) {
     return vcvtq_s32_f32((x + 0.5f).fVec);
 }
 
+static inline void Sk4h_store4(void* dst, const Sk4h& r, const Sk4h& g, const Sk4h& b,
+                               const Sk4h& a) {
+    uint16x4x4_t rgba = {{
+        r.fVec,
+        g.fVec,
+        b.fVec,
+        a.fVec,
+    }};
+    vst4_u16((uint16_t*) dst, rgba);
+}
+
 #endif//SkNx_neon_DEFINED