minui: Add a protected GRSurface ctor.

This prepares for the removal of the default and copy ctors, by making
GRSurface::Create() as the only way to get GRSurface instances.

Test: mmma -j bootable/recovery
Test: Run recovery_unit_test on marlin.
Change-Id: I0c34c3f3967e252deb020907c83acbac8a8f36b9
diff --git a/tests/unit/minui_test.cpp b/tests/unit/minui_test.cpp
index cad6a3d..b188b59 100644
--- a/tests/unit/minui_test.cpp
+++ b/tests/unit/minui_test.cpp
@@ -25,7 +25,7 @@
 TEST(GRSurfaceTest, Create_aligned) {
   static constexpr size_t kSurfaceDataAlignment = 8;
   for (size_t data_size = 100; data_size < 128; data_size++) {
-    std::unique_ptr<GRSurface> surface(GRSurface::Create(data_size));
+    auto surface = GRSurface::Create(10, 1, 10, 1, data_size);
     ASSERT_TRUE(surface);
     ASSERT_EQ(0, reinterpret_cast<uintptr_t>(surface->data()) % kSurfaceDataAlignment);
   }