Make load4 and store4 part of SkNx properly.

Every type now nominally has Load4() and Store4() methods.
The ones that we use are implemented.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3046
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I7984f0c2063ef8acbc322bd2e968f8f7eaa0d8fd
Reviewed-on: https://skia-review.googlesource.com/3046
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/tests/SkNxTest.cpp b/tests/SkNxTest.cpp
index a3aef6b..ce7b5bc 100644
--- a/tests/SkNxTest.cpp
+++ b/tests/SkNxTest.cpp
@@ -317,7 +317,7 @@
     };
 
     Sk4f a, b, c, d;
-    Sk4f_load4(src, &a, &b, &c, &d);
+    Sk4f::Load4(src, &a, &b, &c, &d);
     REPORTER_ASSERT(r,  0.0f == a[0]);
     REPORTER_ASSERT(r,  4.0f == a[1]);
     REPORTER_ASSERT(r,  8.0f == a[2]);
@@ -336,6 +336,6 @@
     REPORTER_ASSERT(r, 15.0f == d[3]);
 
     float dst[16];
-    Sk4f_store4(dst, a, b, c, d);
+    Sk4f::Store4(dst, a, b, c, d);
     REPORTER_ASSERT(r, 0 == memcmp(dst, src, 16 * sizeof(float)));
 }