VideoCore: Fix values of unset components in input attribute arrays

If an input attribute array had a field with less than 4 components, the
remaining components were left unset if not specified by a default
vertex attribute. If neither mechanism would set a component, it would
assume a garbage value.

It has been verified that the hardware behavior is to instead to set the
missing components from the fixed default of (0 0 0 1). The default
vertex attribute values aren't used at all if a vertex array is
specified for that attribute.

Fixes UI graphics on Fire Emblem: Awakening, a small texturing glitch
when selecting a character in Cubic Ninja, as well as eliminating the
unset-W hack which was required for Ocarina of Time to not have
garbled triangles.

This change has been tested against hardware.