Split rsqrt into rsqrt{0,1,2}, with increasing cost and precision on ARM

tests/SkNxTest.cpp

Index: tests/SkNxTest.cpp
diff --git a/tests/SkNxTest.cpp b/tests/SkNxTest.cpp
index 25ece3867be090f013f5d9db3520d2f67d979996..dec7329c2c2e3e44036fb3d62604d1223f25456a 100644
--- a/tests/SkNxTest.cpp
+++ b/tests/SkNxTest.cpp
@@ -50,7 +50,9 @@ static void test_Nf(skiatest::Reporter* r) {
     SkNf<N,T> fours(4);
 
     assert_eq(fours.sqrt(), 2,2,2,2);
-    assert_nearly_eq(0.001, fours.rsqrt(), 0.5, 0.5, 0.5, 0.5);
+    assert_nearly_eq(0.001, fours.rsqrt0(), 0.5, 0.5, 0.5, 0.5);
+    assert_nearly_eq(0.001, fours.rsqrt1(), 0.5, 0.5, 0.5, 0.5);
+    assert_nearly_eq(0.001, fours.rsqrt2(), 0.5, 0.5, 0.5, 0.5);
 
     assert_eq(              fours.      invert(), 0.25, 0.25, 0.25, 0.25);
     assert_nearly_eq(0.001, fours.approxInvert(), 0.25, 0.25, 0.25, 0.25);