common/vector_math: Move Vec[x] types into the Common namespace

These types are within the common library, so they should be using the
Common namespace.

src/video_core/texture/etc1.cpp

@@ -69,14 +69,14 @@ union ETC1Tile {
         BitField<60, 4, u64> r1;
     } separate;
 
-    const Math::Vec3<u8> GetRGB(unsigned int x, unsigned int y) const {
+    const Common::Vec3<u8> GetRGB(unsigned int x, unsigned int y) const {
         int texel = 4 * x + y;
 
         if (flip)
             std::swap(x, y);
 
         // Lookup base value
-        Math::Vec3<int> ret;
+        Common::Vec3<int> ret;
         if (differential_mode) {
             ret.r() = static_cast<int>(differential.r);
             ret.g() = static_cast<int>(differential.g);
@@ -119,7 +119,7 @@ union ETC1Tile {
 
 } // anonymous namespace
 
-Math::Vec3<u8> SampleETC1Subtile(u64 value, unsigned int x, unsigned int y) {
+Common::Vec3<u8> SampleETC1Subtile(u64 value, unsigned int x, unsigned int y) {
     ETC1Tile tile{value};
     return tile.GetRGB(x, y);
 }