neon: add INIT_VECTOR4

used to initialize NxMx4 vector types
replaces initialization via '{{ }}' gnu-ism.

Change-Id: I0da7b3d321f3d48579b7863fb2e4d3f449ae7f5e

src/dsp/neon.h

@@ -33,6 +33,13 @@
   v.val[2] = c;                        \
 } while (0)
 
+#define INIT_VECTOR4(v, a, b, c, d) do {  \
+  v.val[0] = a;                           \
+  v.val[1] = b;                           \
+  v.val[2] = c;                           \
+  v.val[3] = d;                           \
+} while (0)
+
 // if using intrinsics, this flag avoids some functions that make gcc-4.6.3
 // crash ("internal compiler error: in immed_double_const, at emit-rtl.").
 // (probably similar to gcc.gnu.org/bugzilla/show_bug.cgi?id=48183)