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